There are a large class of threads that I call “pointless speculation” (I’m sure some of you can propose a better name for it) that aren’t really opinions, since people are honestly trying to work out factual answers, but don’t really fit in with the “factual answer” type of questions in GQ.
These are circumstances that are totally impossible, like what would have happened if something else had happened in the past, even though it didn’t. Or what results would some impossible happening lead to. That sort of thing. This is distinct from things that actually have a chance of happening in the future.
They seem to be growing in number, and I personally find them distracting in GQ.
I can’t say I’ve seen any notable increase in the number of such threads.
It can be a real judgement call as to what to do with such a thread. Sometimes it’s reasonable to leave them in GQ, such as questions about what the conditions might be in a hole bored through the center or the Earth, even though such a thing is impossible, since the question basically is one about physics.
When something is really speculative, though, my tendency is to move such a thread to IMHO (or occasionally GD if it’s political in nature). Having a thread in IMHO doesn’t mean people can’t post factual information. I don’t see why an entirely new forum would be necessary.
I thought that was the point of “Mundane Pointless Stuff I Must Share”. 
An increase in the number of threads? No, there hasn’t been. There have always been too many of those, but the solutions you listed above seem to be the best way to deal with them.