I don't know that uMatrix will be supported any time soon, but you can turn uBlock Origin into Advanced mode and get much of the same functionality that way.
They're not killing it. Preview/Fenix is essentially a complete re-write of the mobile browser, and they just haven't added all of the extension hooks back into the new version yet.
I think the metrics actually show that most users don't use extensions. But of the group that do use extensions, I'd guess an adblocker is the top one.
"rust-acean"