I'm not aware of any system like that existing on Itch, sorry. And I think as a first-time game dev, I'd probably stay away from that anyway. If I ever start work on a second game after Canticle with some experience behind me, then maybe I'd consider a Kickstarter or other early access options.
well if you decide to fully release this on steam. ill pay in full. last time i bought a game on itch directly; my credit card got hacked. so i have trust issues