The reason for no longer publishing on google play store is that it has become more and more tedious and time consuming to follow their constantly changing terms and conditions especially for individual developers. It’s just not worth it.
I don’t know what valid updates mean but if you don’t trust the source don’t side-load.
If you do trust https://mafa.indi.software you can manually download from updates.indi.software in your browser where you can at least verify the HTTPS domain. (That’s the download link on the home page of mafa.indi.software and it’s the same URL the app uses to get the updates from.)
There are no plans except for keeping MAFA up to date as Android and MPD versions evolve.