This is not a bad suggestion, but, I have an issue with it affecting the forum layout.
An alternative could be the edit option. If changes are made to threads, and the updates could get lost in the replies, the OP can edit the original topic, and bump up the thread so it increases visibility. If users are going to check the first pages to see a reply that was brought up, then they will likely not miss an update on the OP.
The reserve option is also being used and works pretty fine imo.