All "Paladin" means is "someone from the palace," so I'm afraid etymological arguments don't really sway me. Now, to be fair, my "Arcane" is MUCH more elemental than usual. But it needs to include the Sorcerer (Arcane Warrior), Wizard (Arcane Sage), and Bard (Arcane Trickster)--and I don't really consider the Bard an "elemental" caster. I suppose you could fluff it as thunder, 'the fire within' and such, but that pushes "elemental" to the point of meaninglessness, so I don't really care. It seems pretty clear to me that your Elemental is (more or less) equivalent to my Arcana, Spirit::Radiant, and the rest are identical.
Well, no, I don't consider Elemental to be identical to Arcane. I consider power source to be 'SOURCE of power', not power-using tradition. So a wizard would be a Mystic (I wanted to avoid 'Sage' as it implies study). In fact, the Mystic class in some degree corresponds to Arcane, to the extent that it encompasses all characters who utilize overt magic more-or-less directly. A wizard also relates to his power via the tradition of scholarship. In fact wizards, per-se, are really generalists, studying all aspects of magic. I haven't really come to terms with that entirely, is there a separate class that deals with the academic study of each of the power sources? Are wizards just not tied to one source, but instead focused on other facets of magic, such as 'schools', in which case they might all be one theme with specializations?
You could also debate any other choices here. Does the 'paladin' concept need a theme, or is a Warrior class Priest theme basically a 'paladin'? I'd say there's some room for both themes, but my observations of 4e are that the 4e Paladin and Cleric would have been MUCH better if they'd had all Clerics CHA/WIS and all Paladins CHA/STR and made the division much more explicit (IE if you run around in armor and use melee attacks, you ARE a Paladin). That would have avoided two very messy V-shaped classes.
I wouldn't call the Ranger a 'Trickster', I'd call him a Nature Warrior. Anyway, there's actually more ground available in this kind of division than is really needed by the classical D&D cast of classes. I didn't really intend to create a 'grid' of Class vs Power source. You COULD, but some of it might be forced, though interestingly some concepts that are ill-served in typical D&D might come out better:
Warrior - Nature = Ranger
Warrior - Ki/Martial = Knight (many possible minor variations on basic 'fighting man')
Warrior - Elemental = Hmmmmm, not sure on that one, maybe a swordmage?
Warrior - Spirit = Paladin
Warrior - Shadow = Anti-Paladin
Mystic - Nature = Druid
Mystic - Ki/Martial = another one that could be a few things, 'ninja'/assassin, or this could be a swordmage
Mystic - Elemental = Sorcerer
Mystic - Spirit = Priest
Mystic - Shadow = Witch/Warlock
Trickster - Nature = I don't really have an idea for this, exactly, though it seems like an interesting space
Trickster - Ki/Martial = classic rogue types
Trickster - Elemental = maybe another sort of more magical roguish type of guy, or a different flavor of sorcerer
Trickster - Spirit = Possibly an avenger, though 'vengeance' hardly seems like it fits the trickster
Trickster - Shadow = illusionist, though a certain type of assassin also works.
I struggled with the name "Martial" myself. Originally I called it "Body." I definitely want to break away from the "modern" perception that Pure Skill, Grit, And Muscle cannot be supernatural in nature or effect. Hercules is a Martial hero--the fact that he has god-blood in his veins is only a plot-relevant thing, it doesn't give him his powers, not in the way dragon blood gives a (3e/4e/5e) Sorcerer powers. His Awesome Strength gives him powers. Hence why, in my previous post, I noted that the Warlord/Tactician/Captain/etc. has preternatural strategy, tactics that go beyond what Mere Mortals can do. Odysseus, despite not having any godly blood (IIRC?) would be just as epic as Hercules--but as a Warlord/whatever, for he was Ulixes sapientissimus Graecorum. I hesitate to use "Ki" because...well, it communicates an implicit wuxia tone that is not always welcome.
Ki is indeed invested with certain thematic baggage. In some ways it ties in pretty well though conceptually. So I have mixed feelings about it too. 'Martial' lacks the baggage, but has its own 'mundane' implications, as you note. I haven't heard of a third term that splits the difference. There probably IS one, but its also probably fairly culturally specific.
With my (proposed, unwritten) system, as stated, the Bard would be the Arcane Trickster. My Nature Trickster is the Ranger, who uses traps, terrain, and animal companions to harry enemies and coordinate with allies. I've already described the Assassin (Shadow Trickster) and WarTaCaptain (Martial Trickster); the only remaining one is the Radiant Trickster, the Avenger, who works kinda-sorta-ish like the opposite of an Assassin, personally harrying foes and, in so doing, leaving them open for their allies to strike.
For someone who wanted to be....a "more mystical Paladin," well, I'd just say "be a Priest (Radiant Sage)," or possibly pick up a little bit of support-heavy stuff. TBH though I don't really get the impulse to be a "more mystical Paladin." Like...that's like saying I want to be a more science-y "pure mathematician"; if you want to be a science-y pure mathematician, do theoretical science, or comp sci, or something like that--don't try to take a borderline-philosophy discipline like pure math and casually inject some empiricism into it.
Well, like I said, I never liked the "almost a caster, isn't this just a cleric?" versions of paladin either. Paladins fight, clerics cast spells. This actually IS pretty clear back in Greyhawk, the paladin is HOLY but he's purely a warrior, without any significant spell-casting ability.
Forgive me if I'm misunderstanding you, but...are you saying that the DM would need to custom-build each improvement in a character's advancement? Because that sounds like a *nightmare,* for everyone involved, so I'm really hoping I've misunderstood you.
No, I would think that an actual published game would supply a long list of boons, and probably a number of them would include 'guidance' like suggested levels and class/theme/race that they are applicable to. I like a looser system though, instead of labelling these as 'requirements', label them as suggestions. Like put them in sections related to the elements they associate with (martial weapon use boons grouped with warrior themes for instance) but without a rule that says "though shalt not use this if you are a Mystic!" and in fact hopefully the way bonuses are figured and such would make odd permutations mechanically viable, even optimizable.
I'm also decoupling form from function. A boon can be in the form of an item, a magical condition that is placed upon a character, the result of training, a divine blessing, etc. While many boons may best take, and be presented in, a given form, such a flaming sword, the same mechanics could be easily translated into other forms. In other words you might recast the magical flaming sword as an inherent elemental force which a character controls, which can manifest bonus fire damage to weapon attacks. There are some narrative differences, you can't hand your essential nature to another character like a magic weapon, but in a slightly more loosely structured game the two boons would be pretty much exactly equivalent. Again the trick is making the mechanics flexible, so that if a wizard wants flaming magic missiles then ideally the same boon does that and flaming swords. Perhaps that isn't perfectly attainable.
I really haven't come to a complete conclusion on the scope of boons either. Would 'Elemental Mastery (fire)' be a boon? How much would it give you? Does it have fire based powers associated with it? How many? Is it simply a single boon, or are their higher levels of Elemental Mastery with stacking effects? Do these effects scale? If so then you could have stacking for additional breadth (IE more advanced effects) and scaling that just takes care of doing the same stuff better at higher levels. That seems inherently appealing, but you could also design it as scaling with increased variations built in. The question then is more which provides the best narrative flexibility, and which is not too complex. A level 20 PC will have 20 major boons, logically, so each one probably doesn't want to be TOO big of a deal, and yet neither does it want to be so simple that you have to eat up 10 boons to be a real fire mage, unless the game is ABOUT really focusing on one thing...
Choices, choices. 4e seemed to go in that later path, to some extent. You were REALLY encouraged to focus on one or two core tricks, and then you'd have a miscellany of other things you could fall back on, generally. So I've been leaning in favor of powers scale, but boons themselves generally need to be accumulated in order to fully focus your character on a given shtick.
This is in fact what lead me to the idea of boon system, at some level its just skipping several middlemen and doing what 4e might have intended, had someone really thought hard about it.
