Posting in a topic naturally bumps it up, but a feature that allows you to post into a thread without bumping it up would be neat and practical in my opinion.
An example would be the Berserk thread. People are discouraged from posting in the thread through long waits for the next chapter because bumping it up would raise peoples' hopes and disappoint them. This would alleviate that problem.
Or you could post in a stupid thread and not feel bad about bumping it up.