I finally went ahead and tried it... And yes, in the last version of rOS, the old "wireless" package has been purged and the "wireless-fp" package has taken its place, renamed as simply "wireless". During upgrade, both the old "wireless" and "wireless-fp" (if both present in the router) are automatically replaced by the new "wireless" package.
(By the way, this is the kind of explanation that I would like to see coming from you in the first place...
See, I was only seeing a "wireless" package in the files and thinking that if there was any kind of manual package uninstallation work required in order to upgrade, I would like to know it in advance rather than find it out "the hard way", ie after losing wireless connectivity due to a conflicting package.)