On "my system" (there is a default, rules to swap are somewhere else):
I get what I want (a simple default that goes hand in hand with the class)
You have to flip back and fort in the book to get what you want, but hey, you were eager to do it from the beginning, all you lose is some weird sense of legitimacy.
On "your system" (no default):
You get what you want
I get to play a slot vancian caster by flipping back and fort.
This is where I saw your argument boil down to KaiiLurker. If he gets what he wants everyone has to choose the system (or more realistically the DM decides and people all have to build according to that), if you get what you want then only some people do. But if a greater percentage of people dislike the default you like then basically what you advocate for is for a minority to get exactly what they want and to inconvenience everyone else.
all you lose is some weird sense of legitimacy
I had to requote this for emphasis.
You somehow doubt this "weird sense of legitimacy" but that is kind of the topic we are discussing at large. You are saying there is nothing differentiating classes except their mechanics (which I and others have rebutted). You can't call it a weird sense of legitimacy and then say that the only thing that makes a class 'legit' is a certain mechanic.
Also, that is why allowing these options is so key. And why they can't just be relegated to the back sections of the book.
I still get the following benefits from a default:
-There is a baseline, a common ground on what a sorcerer means and can do that allows for a better communication with other people.
-I get the confidence that if an online DM makes no statement about the class is an implicit aceptance, and that any mention to the dial or default set-up beign changed is trully meant and not a guess.
-It get's easy to teach to new players, "this is what a sorcerer means, after you get some experience you can change it if you want to experiment, but for now all you have to care about is the bloodline"
On "your system" (no default):
You get what you want
I get to play a slot vancian caster by flipping back and fort.
I lose the baseline that allowed me to do all of those things above:
-The common ground for the community is lost
-Back to erratic DM behavior (it is not their fault)
-What the hell do I teach to a new player? that many dials are just a run away novice waiting to happen.
-Additionally the sorcerer is back to feeling like empty flavor.
Because it is so difficult to for the DM to say "backgrounds are in, all wizards use spell points, all sorcerers use spell slots and there are no warlocks," or whatever his houserules are? You already said it is not unusual to see huge pages of notes to digest before getting into a game. (It would be for me but that isn't the point, I don't do pbp.) If so, how is one minor change going to drastically change how that game is played? We are talking about a relatively minor change, if done correctly. That baseline you want so badly doesn't even exist between games. I defy you to find anything but a completely newbie (DM, not necessarily players) game and have it work EXACTLY like the game is designed
and how another group will work it. Let me give an example, have you ever played the classic monopoly? What happened when you landed on free parking? Did you just get a square you were allowed to rest on, or did you get money? Almost all games I've played have had the latter option as default, though we realized after many years of playing and enjoying the game that this was never in the rules. In this way, the default may be wrong to most gamers and you want it that way. Whereas Hussar and myself want it to be in the rules, but optionally for everyone. Instead of instituting a way it should be for all games, by default.
And more realistically I've got the feeling things won't get to be as simple and clean cut as you seem to think, so just by having no simple default any chance of getting soemthing simple are gone through the window. The only way I can think of them having a way to balance this is by making different casting mechanics not so different from each other, the sorcerer can be slot based, spell point based or even some kind of AED based, but in the end of the day can only cast spontaneously from a limited known spell list. Wizards can cast form spell points, slots, or even recharge, but at the en of the day still have to preppare a limited set from a potentially unlimited pool of spells known. That is the only way I can think they could do it, because spontaneous is fundamentally weaker than vancian, and vancian-spontaneous is way more powerfull than they think, it just keeps the strengths of both approaches while negating their downsides, an spontaneous vancian wizard gets the power to learn potentially every single spell in the universe and be able to fix things with enough time, and to top it off he no longer fears running out of ammo by prepparing utilities or not prepparing enough of each spell. Fear the unstoppable recharge-spellpoint-spontaneous-vancian wizard of doom!
This may be exactly right, to some extent. Maybe not all sorcerers work with all systems perfectly, and maybe not all wizards can be easily converted to all systems either. However, if the options are presented there at the beginning and with big glowing letters to inform you that the 'default' version is just one option and there are others if you XYZ then that will be a win. Most of the time DMs will like or dislike a system for a class more than the players will probably care. In that case the DM will specify all characters of that class will have a certain system in his games. You'll know that if you are in his games that you'll have to be a 'vancian' warlock or what have you.
It also hard-codes the player to try and play something else, if they like the flavour of a class and the characteristics of that class but dislike the system. If you want to play a wizard and dislike spell-slots, talk to the DM and even if they've said all wizards must be that way; they will still realize that all other systems can work equally well if the DM is willing to let the player play it. I know I probably would, if it is done correctly.
The obvious flaw, as you pointed out, is if things are (A) not balanced between systems, (B) if certain flaws or limits of certain systems can be easily weeded out, or (C) if spontaneous sucks compared to memorization.
For A: That is a real concern, but not undoable. It means that WotC has to do their job correctly so that a wizard with any system is as powerful, in the same ways, as any other wizard. If all wizards use memorization then there should be some kind of limits on that memorization, fire and forget or something, or else the power level should be lower. Those are relatively easy to fix given a variety of fixes and using a variety of systems. This is the part I'm significantly less skeptical about WotC being able to do, as they already partially did it for a previous packet.
For B: In some cases those flaws or limits being weeded out is the whole point. You hate vancian, okay fine then pick from these other systems. They don't have X component you dislike. They may also lack Y you dislike but introduce Z that you are neutral on. I don't think it is a good idea to remote other limits, such as cost, foci, certain material components, verbal, somatic, or any other requirement of casting spells. And if they do then there should be some other balancing aspect to fix that, right out of the box. But lots of times that is the point of switching systems, it isn't a flaw it is the purposeful boon.
For C: I think there are a lot of times where spontaneity makes more sense, should be more powerful, and in general works out better than with memorization. As I've already said, assuming you have a spellbook doesn't mean you get unlimited access to spells. Maybe in a wizard with 3e warlock powers has a harder time learning new spells. Maybe they get less spells per day in that case, ones they have to choose at the beginning of the day, but can cast them far more frequently. These kinds of issues are harder to predict outside of playtesting. But fortunately WotC has a handy playtest going on where they can try and figure some of these power levels out. Worst case scenario they end up giving the wizard too many spells or the sorcerer too few (or something like these of course), in which case you can fairly simply increase the sorcerer's slots (again adjusting for mechanics) and/or decrease the wizard. If this is happening at large that is a flaw by WotC that shouldn't get into the final product. But if it is something only happening in your game then maybe you have different expectations and realities than WotC does and need to adjust accordingly. That does sometimes happens, but hopefully with a superior product where everyone can get the system they want everyone can be equally happy. Instead of making one person happy and not allowing anyone else that level of legitimacy.