I think all this discussion is extremely premature, because WotC is working on material which does this.
My understanding is that Level Up wants to remain substantially compatible with 5E, yes? That all WotC material should essentially remain usable. Given WotC are working in exactly this design space, I think it's an outright bad idea to even start working on stuff here, until what WotC is doing becomes clear.
There is not much worse, for my money, when you get a third-party product which covers the same ground as an official one, but does it differently, and often both have hard-incompatible or significantly incompatible approaches (which is extremely likely to be the case here), so you have to pick one, and they probably both have serious weaknesses or things you wish the other had. Whereas if you just wait for the official material, you can work from there, and do a better job - support whatever areas it is weak on, expand areas where more material would be good, and so on.
Chucking around ideas is fine, but locking yourself into them or getting a really fixed idea of what Level Up "should" do in this space at this point seems like a very bad plan.