>If I install some distro, Arch say, and I wanted to use Sway, and I then want to run Kile, will Kile then run through XWayland?

Kile seems to use Qt5, so should work without Xwayland.

> Will it work just as well as Kile on KDE Neon?

It should, yes. I don't use Kile though, so I haven't checked.