But the Vancian spells are the ONLY class feature of the 5e wizard (unless you count "spellbook"). Familiars, class skills, etc. are all handled through background and theme. I'm guessing that the other "pure" spellcasters will be similarly stripped down: spells as the primary component of the class, with minor class abilities handled through themes. (Or feat selection, if you're ignoring themes.)
And that is a problem with the Wizard's class design.
Let's say I'd want to play the Wizard concept, but using the Cleric's spellcasting system (they're pretty similar, but I'm just using what we have, here). If I'd just need to take the Cleric and call it a Wizard to make it work, the following happens:
My Wizard has less spell slots, overall.
It can freely choose which spell to cast from the list of prepared spells (what I want).
It has.. "Channel the Arcane", which at first allows me to repel the undead.
I have spells not really fitting for a Wizard (such as cure light wounds).
I can now cast spells while wearing armor, and receive much more in the sense of weapon proficiencies.
I now suddenly use my Wisdom instead of Intelligence.
Now I can change some things, like making spells work off Intelligence, but overall, I get quite some things not befitting a Wizard.
You could say I shouldn't take the Cleric, because it uses 'Divine Magic', but that shouldn't matter - it's the spellcasting system we're talking about here, right? The point is, that the Cleric has all these other things that have nothing to do with its spellcasting system.
Also, what if I want to play a Cleric that uses Vancian spell memorization like the Wizard?
I really don't get what you're asking for here. Are you saying they should do multiple complete versions of every class, like rewriting the 5e wizard with 4e-style AEDU powers or magic points, so that you can mix and match your favorite flavor caster with your favorite spell system? Because that's more or less a complete rewrite of the class, i.e. a LOT of work, and honestly I'd rather see them spend their time making, say, the Psion class than jury-rigging the Wizard class to use magic points.
No, I'm not saying that at all. That would be exactly what I don't want.
I'm saying that spellcasting classes shouldn't be married to any spellcasting system.
Write the Wizard, or whichever spellcasting class, with its own special things, and then leave it open which spellcasting system you want to use.
Balance the different spellcasting systems so that it's internally balanced.
One class might simply get more spells, and that could be (part of) their special thing, but that doesn't have anything to do with the spellcasting system.
You're saying you'd rather want the Psion than having them force spell points as an option for the Wizard.
If the Psion is no more than a Wizard with spell points (as in, has no special features of itself that makes it different), than you have exactly what you thought I wanted to have.
But, if on the other hand, we have a Psion with its own special features, I can't make a Wizard with spell points by renaming the Psion into the Wizard, if that's what I want to play.
So, instead, I would say make the Wizard, make the Psion, but give both of them special things, and leave the matter of which way they cast spells open to the player.
The Wizard's 'thing' could be the collection of spells into the Spellbook, and getting more spellslots (or spell points, or whatever) than other classes.
The Psion could get something special that reinforces its mental prowess.