This is a bad idea from a user perspective. The last thing I would want is to get home after work and find my inbox flooded with multiple emails from the same topic. They may say they want it but believe me, they'd soon be crying for a change back to how it is now after a few days!
What's the problem with them visiting the forums in the first place anyway?
I totally understand that, and I wouldn't want a message every time on some big forums. But for our forum that feature would be perfect because it is very niche so there are only a few replies. So can it be done please?