I think this is agreat idea. I know that lots of my threads or thread I have posted on have died because I have forgotten about them. Which sucks for me because I love to roleplay, and some roleplays have amazing plots.
Also people are always saying bookmark the rps but not alot of people can do that if they share a computer, like me for example.
And the alert you get after someone post on one of your sucribed threads is an amazing idea.
You have my full Support.