Personally, I don't like that idea at all. This is supposed to be a supportive environment, but what you are proposing screams "you are only worth our help and support up until a certain point." Many people here have histories of experiencing emotional trauma upon discovering that love they thought to be unconditional actually had conditions. "We're here for you and we'll support you...for problems 1-5. After that, we don't want to hear about it" doesn't seem like the kind of attitude that would be helpful for these people (most of whom probably wouldn't post more than 5 new threads, anyway. They just need to know that the option is available should they ever need it. )

I usually check page 2 in a section if I don't recognize the last few posts at the end of page 1. I doubt that I'm the only one. If someone feels that his/her thread is being held back, then s/he can always add another post to "bump" it back to page 1.

Rule addition always makes me feel severely uncomfortable. I think we ought to be searching through the rule book to see what we can cut out, not looking to put more restrictions (that are often seen as unnecessary) on peoples' liberty.