Such a feature would be nice.
It's been rumored (and somehow I lost umpteen hours of time this summer) that we're working on a move to Jive. Jive will have some nice features (such as the one you've requested) and since it's a
Java web-application, we'll be able to (more) easily configure and fix it to our liking.
In the mean time, I (and you probably) can just look at the "Last Post" time stamp and try to remember when I last looked at the
thread.