I’ve seen this said a lot, but I think it would only happen if the extra queue is implemented badly. (An opt-in system just consists of having 49 extra ques.)
Now TBH I wouldn’t trust FE to implement extra queues well. Seeing what they did to the prefered map option, and to team game ELOs. They’d have to consult with someone who understands game-theory… But if they do they could implement extra queues without driving everyone to a small set of maps.
Remember the ranked map pool already drives players to play on a set of 7 maps, and this is mostly a good thing. It keeps queue times short and it doesn’t get stale because the maps rotate.
There’s an entirely separate argument that having an ELO which labels your general skill is good, and being encouraged to improve on maps where you are weak is nice. Matching with players who are the same ‘general skill’ as me but better Arena players is useful as a yard stick, to show me what I can improve on Arena. All this would be lost with an opt-in system.