Was thinking about moving to sargeras, but I dont ever see it "full" but always high, how bad will the queue be on the release of BFA?

It'll be full but it won't be que as bad as servers like dalaran and illidan.

Right now it's medium-high pop depending on time of day. It'll be high-full come bfa

queue will be pretty much non existent, MAYBE a 1-2 min queue.

Immediately following launch is a different story though, after the first day won't be an issue.