Hers the thing...op and voice are the only channel modes (user) that are in the rfc, so all ircds HAVETO support them (whether they are @ and + is for the 005 numeric to determin...but thats for a diffrent discussion). hop, uop, admin, owner and scores others have been implemented in unreal, ultimate, etc (the socalled "RFC busters"). If you are going to support one, you might aswell support them all.
one way would be to make the entire thing dynamic. remove auto op/voice, and replace it with an auto mode setting, where you pick what mode to give a user on join (any in the 005 would be supported then)