I support that idea. (the same could be done for all other engines I guess).
Question is how many people would regularly engage in discussions about a specific engine. I guess, not so many, as others have put it before.
As long as the official forums are good, why not post engine specific questions and discussions where not only most of the community, but also the engine devs are?
Maybe split the engines dsicussions out of the API forums. Currently, you really need to read the description to see that engine specific discussions should go into the API and tools forum.
Forum tags could take care of making sure people would know what engine is spoken about, and if people would like to post more generic, engine related question like the "which engine is best for X", they could do so there while reaching users of multiple different engines.
Would make sure the subforum is more populated too. How many people here are using lumberyard? I am sure there are some. Are there enough that the forum isn't becoming a wasteland?
For example it seems the amount of artists on this forum is rather low compared to the programmers and designers. The art forum gets regular, but low traffic. It is only thanks to some people actively "haunting" this subforum and trying to answer questions that pop up that the forum is not completly deserted (thanks guys, you know who you are).