It is superseeded by the Purpose integration in Dolphin
Is there/should there be any provision to remove it if it's already installed? Or is that something that distros should/would/will take care of for us? If not, I worry that people with KDE Connect already installed will see duplicates.
Sure it will, at least in all packaging systems I know of. The issue here is the time between one update and the other one, when there would be two plugins (if purpose is updated first) or none (if kdeconnect is updated first). I'd suggest to bump KF5_MIN_VERSION to 5.48 to at least prevent the latter.