Knowing what I know of what the scope is for 5e in regards to class design, this is what I’d do if I were on the team, and what I think they are doing:
archetypes should be handled as subclasses whenever possible. With how 5e is designed with subclasses, feats, and skills, this is largely entirely possible.
Outlier classes are generally tied to a setting, and when creating that setting, a new class can be created. See the artificer. First class in 5 years. Pretty much Eberron specific. I.e., hard to have an Eberron setting without it. What this does is allow tables that want the class to have it, but not force AL table DMs to accept it if they don’t want if they aren’t playing in Eberron.
I think the psion will see the same treatment with a dark sun setting. Hard to have a dark sun setting without a psion. But for those who don’t want the psion, they don’t have to unless they play in a dark sun campaign.
Crawford said they probably won’t create new mechanics for a psion because hardly anyone used them in the past, and it’s a design requirement to keep rule variations simpler, and available to the most players. So I can see them creating a new psion class for DS, but most likely would either be modeled after the warlock mechanic, or spell point sorcerer mechanic.