Hi, this is Kai from the Cider Discord server.
Firstly, the MS Store version is not abandoned! Due to how Microsoft processes updates, it does take a long time to have anything update on their side. This is one of the major factors as to why Cider hasn't updated anywhere, we don't want to release an update everywhere BUT the MS Store! Keeping that in mind, we want to serve large, quality updates, which is also why there has been a large wait time, we have a lot of new features coming! Next, Itch.io is the latest and last storefront Cider is going to be released in. I understand that having different storefronts every few months is infuriating, trust me it was a hassle to try and get Cider on Steam (which was ultimately rejected by Valve). However, Itch.io is going to be the definitive store front for those looking for a one time purchase to get Cider on all their platforms. As for migration plans, it is a huge hassle to have every MS Store member have their license transferred, so unfortunately that is out of our scope.
Hopefully I could help! If you have any other questions feel free to open a support ticket in our Discord Server!