I am against this if only because... I don't feel the captain should have 100% say in a team. If you really want three engineers but someone really wants to be a gunner, I think you should have to find a compromise.
It's why I am happy captains "suggested items" isn't a forced function... I imagine many people wish it was..
Could always have a "suggested class" thing so the person has something on their screen saying the captain whats them to be a different class, this may help with language and other barriers in communication that happen..
I agree the trolling potential is no higher then many aspects of the game.. So isn't really an issue, the captains who use it, if added, to troll, are gonna troll regardless in someway.
I think a better solution to solve most of the issue(mainly getting stuck with two gunners), is just default ships to one pilot one gunner two engineers, when MM makes it.. If there is to many gunners, simply suggest they change to engineer to find a quicker match.
This would solve "most" issues right away, since people who will play gunner or engineer.. can willingly switch before they even get to the lobby..
People who want to be a gunner no matter - can just wait for a game where they will get to be one.
Muse already said they could do it easy in one of the fireside chats, they just don't want to .. So it should be easy to do.. or at lest very possible if I misremember words.
I don't think a captain having to not have three engineers is an issue necessarily. I do feel two gunner ships is a balance issue that can be addressed... More so in novice or lower skill games then higher skill since.. I've seen two gunner ships do good .. but its very situational..