I don't support. I've stated my reasons on the already locked forum but I'll put them up here again anyway.
This will encourage necroposting. Many users would be able to find a thread they'd like and often they won't check when it was last posted on. For example if one would search 'wolf RP' the most recent one might be one that hasn't been active for three months. They'd post a follow up to the RP and then they'd just be bringing back a dead topic. Which is annoying.
I think this porblem would also occur a tad more in the advertisements forum. If one would search 'omni' in the ads; they may come across an old thread where an omni was being sold and hadn't been updated that it had been sold. A user would just unwittingly post there.
Though this is useful to some people, it may bring up new issues. I highly suggest you just bookmark a thread you're watching.