Highlight Zombie thread date
Recently, have read several zombie threads and even contributed to one (from 8 years ago, I think). Suggest that in the thread listing, threads in which there has been no activity for some time (6 months?) have the date highlighted in red and bolded. If you want to get fancy, you could have a "ZOMBIE THREAD" watermark in the reply box (which would disappear after one typed a certain number of characters.
Could save Forum users' time.