It is not that it isn't appropriate for D&D it isn't what I want in D&D. So if you are asking what I want in a 6e, then metacurrency is not going to be a part of it. Can metacurrency be a part of it - sure, but that is not something I want in the core game. I want the core game to fun and tactical without metacurrency.
Though at this point I guess we need to define what we mean by metacurrency. I don't consider things like spell points, slots, maneuvers, etc. as metacurrency. I do, generally consider things like inspiration, hero points, action pionts, fate points, etc. as metacurrency. Admittedly it can be a fine line on some things.