I like that idea

I'll think about that when I'll be working on enabling post edition/deletion for users.

I don't know if this is good idea though, this and editing usernames raise some concerns for me.

understandable as to why that would be a concern, but please give it some thought, thank you for replying as always boss

If it raises concerns you could always make it so that every user has a tag they can't change

It would probably be best to keep topics as "Once posted, it's done" for database, archive, and searching reasons.

I'd have to agree with @Joker and @Mishima on this. But what @HahaRIP said also sounds like a good idea, but I feel like it would take away from what makes a forum a forum. Feels too Twitter-esque to me.