I have been using LiberaPay for a while (started using it just before the issues with (I think) MangoPay happened) and because of their dealing with stuff with MangoPay, they went through some process that they found that they were not able to offer a "wallet" system, any more. I'm not quite sure what the issue really was, but in essence in order for them to *legally* be able to offer a wallet system, they would have to be declared a bank in at least one country, and quite possibly in a country which deals with any currency they deal with.
I have no idea which project would be considered to be more capable of handling this. I'd really wish there was a way that it could at the very least be a short term option, ie. with Patreon (which I also deal with) they allow the possibility to pay out to the creators you support, with the money you make from the supporters who support you).
If that were an option, and they could say, "money not paid out within X days, reverts to itch.io" or something it would be something that could work out reasonably well. I'd *love* to have that X be 90 days (not that I'm doing stuff here that would make it an issue). I think the problem with that, is that it would require setting up some accounting to deal with figuring out how long, "that" money has been in the account.
I do think that the problem is *probably* a matter of it not being a priority. Though there are technical/legal concerns that do come up which would need to be addressed in any such system.