Upstream images vs bazzite: https://github.com/ublue-os/countme/blob/main/growth_upstream_with_bazzite.svg
My prediction: bazzite may have more installs than Fedora KDE by the end of the year.
Everything is possible. The point of immutability is the ability to restore to "factory fresh" state with a power cycle.
In theory, the data section is treated as data only, not executable. Software (games) can, and will, improperly store and execute code there, but at least they can be identified when they do and disabled/removed without breaking the underlying system.