https://en.wikipedia.org/w/api.php?action=help&modules=query%2Busercontribs
uctoponly: Deprecated
ucshow permits top and !top options as a replacement. This is not consistent with other modules:
I propose these be deprecated in favor of wlshow=top, !top and rcshow=top, !top .
More specifically, ucshow=top is the replacement. ucshow=!top is the companion, to show contributions that aren't the top revision. The default when neither are specified is to show all revisions, top and non-top.
Deprecating the recentchanges rctoponly parameter in favor of rcshow=top is straightforward, I don't see a problem with that.
But replacing the watchlist wlallrev parameter would be problematic. To duplicate the existing behavior, wlshow=top would have to be the default. Then when a client passes a wlshow without including top, how would the API know whether the client really intended to not include top or if it's just an old client from before top existed that wants the old default behavior?