For quite some time nova has been pushing up against the connection limit on m5. And we're about to add a few things:
We're about to add a new (required) service, which will may increase the number of worker connections yet again. If we could get the limit boosted to 1.5 or 2x the current number then we'll have room to breath and won't have to spend time balancing worker count vs. connection limits.
(And, I concede that it's weird that nova needs so many connections, but short of re-designing nova entirely I think we need to live with it. It sounds like most other nova deployments use 10x the connection limit we're running).