If you mean the ones in the Area Box I see no reason to limit how many because of the fact most of those are still under construction/need of tweaking.
Not counting Guild threads, we have:
2 play threads for Desolate Lands
5 for empire state
4 Paradise Threads
2 Shina Ania Threads
And 2 islands.
We have a total of 11 play threads, which for something that's supposed to be an entire world of its own, is severely limiting. So placing a limit on how many are made for these regions sounds counterintuitive if we want diversity aside from "This is a place for you to fight things that randomly appear." Because not every character made is necessarily one equipped for a combat roleplay.
I can agree to limit the kinds of threads that are there solely for people to use as a battlefield, but overall the ones that need more diversity would be any regions that aren't Empire State, which has threads to fulfill its niche for the most part. We could use more variety in the type of threads made. Say, a trading town instead or a watering hole with healing capabilities placed in areas like Shina Ania or Desolate Lands. I'd like to see more variety in future threads besides the thread serving as mainly a place to get into PvP scuffles. We can't develop lore for the regions if there are very little threads made to serve more than just a site for fighting.
The limit I'd place at most is creation for Empire State, since there's not too much left to make threads for in order to develop the history behind that region.
MMerging character threads into one would definitely be easier for the OP to find their character info.