Multiqueue was actually enabled at Nost release and was removed fairly recently. I think they disabled it sometime in September.
Some brief background info for you - in early August an unrelated change was made to the BG queue system that caused Premade groups to be placed in a separate queue where they only faced each other. People quickly realized that if they queued as a group for both AB and WSG, and the enemy premade did the same thing, then each faction could join 1 BG and play an empty "free win" game with no opponents.
This wintrading was very widely abused for about 6-7 weeks before multiqueue was removed as a band-aid fix. Level 60 PvP is definitely much, much healthier without multiqueue. They still need to remove the prem v prem separate crap, because it has made ranking no longer competitive, but that's another story

The short answer to your question is, if there is a way to enable multiqueue only in lower level brackets, that would be nice... but it is disabled for a reason and needs to stay disabled at 60.