There are pros and cons with both solutions. Initially I really disliked Epic’s decision to have a joint forum. But things are already starting to settle down I think. Yesterday, half of the threads in the Engine boards were stray UT threads. Now it’s only a few.
I think, once the wave of enthusiastic gamers disappears, who have no intention to contribute to the project, we will mostly have regulars who can tell apart the UT and UE boards. And at that point, it’ll be more convenient to have both topics on the same forum, since a large part of the communities will probably be the same.