It sounds logical, but a quick scan of the top 135 threads in the Scifi forum shows the following:
Threads Topics
19 40K
12 Star Wars
6 Rogue Trader
5 Battletech
4 Dune
2 Dr Who
And there are some others that popped up regularly too, such as Star Trek, Aliens and the Quar, but I didn't count those (it's a slow day at work, but not
that slow

).
So going with the above results, it seems the first universe to get its own sub-forum should be 40K (and related topics; I included Epic threads here as well, but left out the specifically Rogue Trader ones).
While I would not be categorically against such a subdivision, I personally feel that it would do several things which might be undesirable:
1) Threads/Posts would get less views and comments, since there would be fewer people finding the content
2) It would isolate/bubble certain topics even more, preventing cross-polination and influx of different ideas
I for one really like the diversity of topics in each general forum; it often gives me ideas and exposes me to subjects I would not seek out otherwise, or even know about. And to me, that's a good thing.
Previously, we had sub-forums created because certain topics would innundate/flood the general forums, to the detriment of threads with different topics. For instance, the Frostgrave sub-forum over in Fantasy, which was necessary at the time the game came out because every other thread was a Frostgrave one. (although traffic there has slowed down considerably since then; just saying). But this is clearly not the case with Star Wars related threads.
So, all things considered I wouldn't make this a hill to die on but I would probably prefer things to remain the way they are now, especially considering the bit of inventory I did just now
