Thoughts - I fail to see how the Artificer couldn't be made into a group of subclasses instead of a single one painted on top the wizard. One kind of artificer will certainly work on the wizard. I suppose another kind could be on top of the bard. A third as a Rogue, a fourth as a variation of Fighter. Taken together, you'd have several different methods of pulling off the artificer.
Psion, at its base, works very much like the 5e sorcerer does, just with CHA instead of INT. You have the points and metamagic to make it work like a psion. Just need a few more spells, and its very close. Other psionic classes? The monk can have a psychic subclass, as could the paladin, and maybe others.
The warlord? When people talk about the warlord, I've found its not because they can't play the 4e core class warlord, its that they can't make the lazylord specific build - the 4e class in the core book did need to hit stuff still.
See, here's the conclusion that I've come to about the different 5e classes. The only thing that separates them from other classes are mechanics. Flavor isn't enough - that's what individual subclasses are for. The only thing that matters is the class features.
I would have thought that flavor mattered at all, but then they came out with the Favored Soul for the Sorcerer. That alone made me stop and shake my head at my old presumptions. If a class flavored as a divine caster, blessed by the gods, is sitting next to the arcane dragon bloodlines, then the only thing that matters is the mechanics. While there's a feel to each class, its all really flexible. So, for the sorcerer, the only defining features are the full caster-hood, metamagic, spell points, and how to learn spells; neither the spell list and item proficiency even matter much, considering how easily both were added. Hit points? Dragon sorcerer added some easily, the +1 hp a level effectively bumping up the HD.
So, when we look at the warlord, psion, and artificer, I ask myself - what do these three have in the way of unique mechanics? The psion was defined by spell points, which we already have in the sorcerer. That's not enough to make it a new class in 5e. Warlord? Well, the lazy'lord? Never attacking yourself, giving your actions out to others, while never using spells. Surprisingly, a better candidate for its own class over the psion, but at a loss for any variation in its execution, as well as problems related to party composition - asking for a basic attack simply doesn't work in 5e, given the vastly different classes in play and how they work.
Now, the artificer. Its defining feature is "magic item creation / use." Already, we've run into issues with the game. Magic items are meant to be rare. 6 permanent items over the course of 20 levels, plus random consumables. 3e also allowed all crafting feats at once, and just allowing magic item creation in a game that puts it generally in the "optional rule" territory is huge.
In 3e, the artificer could make magic items to do anything, and carry all of them, not a problem. In many ways, they were another symptom of CoDzilla type situations. That is going to have to go. Sorry, but any artificer class will need to be toned down, so it follows the same attunement and concentration rules as everyone else; we're going to have to balance on par with everyone else. If you think that artificers should break those rules? Just... no. Their golems? Its been compared to undead in the past, and I don't see why it can't be a new spell or two for constructs. Bane Weapons? Someone mentioned a variation on the Elemental Weapon spell. Pull out any spell to a problem - actually, this is one of the major defining points of the wizard.
In 4e, we're looking at a healer, a buffer, and a golem master. They get rituals, including the one to make magic items. Magic items that could recharge and heal.
When you combine the two we have... someone that makes magic items (for self or others), golems, and some healing. All of which are effectively just signature spells for the artificer. What else is there out there for the poor guy?
This is the real reason why I'm on the subclass bandwagon. While they ooze flavor, that's not enough for a class. There needs to be mechanics. And I'm hard pressed to come up with some unique mechanics that isn't already covered already, or easily reproduced by a small number of spells.