I don’t really understand Canonical’s decisions. Early on Ubuntu really did make things simpler, but now days most distros have caught up in terms of usability, and now it just seems like Canonical tries to do things differently for no benefit. (See trying Unity, but switching back to Gnome, or trying Mir, but switching back to Wayland.)
When they say “Ubuntu Apps”, I guess they mean their handful of custom written programs, like Ubuntu Apport or the Snap Store (and then only future programs similar to these), so I guess, this decision doesn’t actually have much of an impact.
At this rate, we’ll see maybe one or two applications written in Flutter until they change their mind again.