Personally I don't care what we call them, but I *do* care about consistency. Stem continues to call them Hidden Services because nobody has offered to take ownership of renaming all the things. For instance the tor, spec, and website codebases still heavily use the old name...
torspec$ grep -i 'hidden service' ./* | wc -l 105
webwml$ grep -iR 'hidden service' ./* | wc -l 369
tor$ grep -iR 'hidden service' ./* | wc -l 1054
... and this doesn't count the dozens of other codebases we have, aliasing torrc parameters, aliasing controller methods/events, etc. Personally I really like Sebastian's idea - hidden services are the name of the old thing, and onion services are the new thing. This avoids a lot of headaches.
That said, renaming is certainly doable. It'll just take someone interested in investing days to hunt down all the old things and make pull requests. The one course of action I *do* object to is saying "we've renamed these to Onion Services" without actually changing all the things. That's just confusing for our users.
Cheers! -Damian