I'm not sure if that's sarcasm, but we certainly can.
Yes it is sarcasm, because my intent is to belittle the concept that we need to SPECIFICALLY make casters more special than everyone else to get the same effect. Really Mearl's article feels more like a piece of apologetics for gutting certain core design principles in 4E. For example we can extend many of the ideas in this article to the really strange decision for shades/vryloka to pick up racial penalties out of whack with every race in the game. The Vryloka at low levels suffers pretty heavily from my own testing early on - coincidentally when PCs are most likely to die and not have access to raise dead magic. A race that is tragic at low levels and balanced by increasing power reminds me of something.
Could you remind me of what that something might be? Incidentally, I think it's poor design and it's one of the reasons I no longer play that. One thing I loved about 4E from the start was the inherent balance in the system. Your level 1 Wizard contributes just as much as the level 1 fighter - not just his 1 spell in whatever encounter swung on it or not. What else I loved? Your level 30 Fighter
contributes just as much as the level 30 Wizard. Now that was novel. For me, without epic experience with essentials classes (but plenty with things pre-essentials) I can't say how a Slayer would contribute at epic tier in any manner (and one off playtests at epic are frankly very poor for assessing much beyond vague conclusions or ideas) compared with a level 30 mage.
But my personal suspicion is that I'd rather the level 30 mage to the level 30 slayer. I don't need any "suspicion" at all to tell you who I would far rather play though: Give me the mage over the one trick pony (basically a charge spam build - albeit a REALLY nasty charge spam build) slayer every day.
It could be an encounter where the rest of the party has to hold off a continuous stream of attackers while the fighter makes Strength checks break down a door, or the rogue makes Thievery checks to unlock it so that they can escape.
Both of which are things that skill challenge like mechanics can already easily accomplish. These same convenient mechanics can also cover the same situation as needing to finish a ritual during combat as well for whatever reason/effect.
In fact the last time I ran something like this it was almost "capture" the circle. The PCs had to fight endlessly respawning enemies while defending a partially complete magic circle against undead. The goal was to complete the magic circle while fighting the undead off. Unlike the general way these are done, I didn't force PCs to use their standard actions and allowed thievery/religion/arcana as key skills in the challenge for completing the ritual. Although every PC could only make 1 check a round maximum, I allowed anyone to make checks and gave bonuses based on what they gave up. Firstly, making any check gave an OA as the PC had to bend down and otherwise pay careful attention to what they were doing (making clearing off the undead essential).
A PC could use a minor action and end up with a -5 penalty to their skill check. Additionally OAs against them had combat advantage for the attack. This was literally a desperation move.
A PC could use a move action and make their normal skill check.
A PC could sacrifice their standard action - a big commitment because the challenge required a considerable number. This actually gave the PC a +2 circumstance bonus to the roll in question and added two successes - not just one. There was no 'fixed' failures or similar nonsense - the penalty for failing it was ever increasing risk of being utterly mobbed by undead (and a longer, more resource draining combat). Suffice to say it worked brilliantly, was thematic and everyone contributed.
Everyone. Nobody was told "Sorry, you're not a caster so go sit in the corner being useless" - because even the fighter, albeit arguably being yelled at by the nearby cleric what to do, managed to successfully figure out what all the various lines did and completed a key part of the ritual. Best of all he did it on a minor action, while bloodied and almost dead. Of course the wizard and cleric finished the job off - but the point was that valuable contributions across the party were had and an intriguing encounter was made.
So why do casters or - frankly - anyone have to be special
by the rules to make an encounter like that engaging? My sarcasm is simply intended to really dismiss that concept, as I don't see any valid argument anywhere for that kind of "non-balance" being required. I mean metamagic and similar ideas sound interesting, but I don't see why they can't be applied universally like in your last point in your post. If it works within the AEDU structure that's even better - of course noting that there are lots of flaws to the kind of structures proposed.
For example doing +4d6 damage on a power in 3 turns might sound interesting, but it's actually pretty worthless because an extra 14 average damage on an attack doesn't compare with 3 rounds of 1d8+mods. When you consider that 1d8+4d6+mods in 3 rounds is actually going to be far less than 3d8+3*mods damage - these ideas are far off the mark of being balanced. You would need to compensate for them massively, particularly to get over how much you lose in the 2 rounds trying to cast it in the first place. On the other hand, in the case of characters without a high amount of static damage - I'm thinking many controllers as an example - certain ways of structuring this like the below benefit them too much. Without the risks that certain people think would be implicit. If it takes fixed rounds to cast, being hit in 4E is so hilariously common that these powers are practically worthless. Skirmishers in particular will have an absolute field day with you.
I personally think that the 4E engine is able to handle something like this. One possibility is metamagic Encounter attack spells that cost a standard action and basically grant an Effect: You gain a +4 power bonus to the next attack roll you make with an arcane attack spell before the end of the encounter. If you hit, you deal + 4d6 extra damage. If you take damage before you make the attack roll, you gain a +1 power bonus to the attack roll instead, and you deal +1d6 extra damage if the attack hits.
There are several flaws with this, the first being that in a game with action points for extra actions the penalty on taking damage can be rather irrelevant. You can use it and then dump it in perfect safety - barring a creatures reaction. Let's take an example:
If we have an at-will power that deals 1d8+16 damage and have a 65% chance to hit, with a 2d10 crit effect (staff of ruin for example) we end up with:
((4.5+16)*0.65)+((24+11)*0.05) = 15.075 DPR.
(Average d8+static mods multiplied by hit chance) plus (maximum damage on crit plus average damage of crit dice) = total DPR.
Using an AP and attacking again with that at-will we get an overall 30.15. That's not great really, but we did attack twice so who cares.
Not spectacular. Now if we use the above we get very different numbers. The +4 to attack is effectively adding +20% accuracy. 4d6 averages out to 14 extra damage. The metamagic power is used, then immediately employed by using an action point to attack with it right away - ignoring the "balancing" disadvantage you've supposedly built into it (whoops).
((4.5+16+14)*0.85)+((24+24+11)*0.05) = 32.3 DPR.
Barely above just using the at-will being used twice with both APs - so is it really that bad then being able to do that? Looking at the numbers, what should stand out is the 80%+ hit chance as the advantage on basically never missing is fairly obvious - especially for a controller or similar character wanting to impose an effect more than DPR. The point here really isn't to get obsessed over the hit % I picked, but note how big the +4 is as an advantage and just how much that impacts the damage - almost as significantly as the extra 4d6 in fact. The problem is that it's risk free except for needing the standard action. If you need to hit and deal some extra damage, you aren't going to lose much over the at-will here (noting that if static mods are higher, you will - but I'm thinking of a non-strikery controller really). In a game with action points, this sort of "risky" decision is no longer risky and instead becomes just an incredibly powerful option.
As a mechanic it's interesting and has merit, but it's not something that should be tacked willy nilly onto existing classes. A new class that limited the feature and prevented abuse from action points (or extra actions in general) would work very well. It has great merit as an interesting kind of striker mechanic though, but would need to be carefully thought out on how it worked and fit in with the rest of the system.