I have a similar idea for managing contacts where the contact is "bumped" up whenever any type of communication is made (send/receive phone calls, emails, SMS's, etc)

Less important contacts naturally settle to the bottom. You can scan the list once in a while for people you've neglected but wish to keep in touch with.

Interestingly, KakaoTalk, a popular messaging app in Korea, organizes your chat rooms like this and I use it much more than the alphabetical list of contacts.