In this photo on a game forum I use, when adding a reply before someone has replied after you, your response is automatically added to your first one.
I feel like, if this could be implemented, it would definitely help cut back on double/triple posting and whatnot.
The only downside to this, though, is that if you have an art gallery (like me) you can't double post, so I have to delete my first message and then repost. Obviously, we don't have that option here so it could maybe be excluded in subforums where double posting is okay.
Apologies in advance if this has been requested, but I didn't find anything like this and it's a very specific spam prevention method.