The truth is... I've been thinking about it. The problem is that itch doesn’t naturally allow payments. Unless you're part of a bundle, it's really hard to make money, because the moment you change your page settings to accept donations, you get deindexed, which basically means your game becomes invisible, and the only way to find it is through a direct link.
The game’s currently at version 0.5.5, and it’ll probably reach 0.5.6 in about a month... Maybe I’ll upload version 0.5.5 here next month and leave it as a "demo", and then have all the updates on a completely new page, but only for paying users. This page would just stay as a demo to redirect people to the latest version.
That’s basically the only possible way to do it on itch right now... but I still haven’t decided.