Yeah, that's the fun part. Hooking into some auto-update mechanism would be useful to me.
But my stuff is mostly in the scratching-my-own-itch stage, so setting up a FlatHub account, Flatpak metadata, sandbox rules, probably an icon and screenshots and whatnot, and automating the build+releases, just to get auto-updates, yeah... no.
I could code a whole nother project in the time that would take.