I sometimes hear that someone doesn’t want to post an idea because they feel like they would have to write a whole post, and it would need to be long, complex, and fully fleshed out.
I think short and simple Forum posts are fine — in fact, it’s often better for a post to be significantly shorter. (You could also consider making it a Quick take.)
I agree with this concern, and that splitting is a possibility. But in the meantime, given current traffic, it could be worth considering making the frontpage a little denser, to fit like 50% more posts...