Hi PowerGlove!
I don't know if this suggestion has already been made, if it's doable or not, anyway, I submit it thinking "we never know.." :
I'd love to have an option when sending a PM like "self deletion in x days".
I always delete PMs I receive once I've replied to them, and the same goes for those I've sent once I've got a reply from the recipient, for privacy reasons (for example, I frequently receive names, addresses, phone numbers and other personal data).
The problem is that if people don't delete my PMs on their own, or their own sent PMs, they're always a potential source of trouble in the event of an account hack or other incident (type Bitcointalk's hack etc..)
I think that as long as the self-deletion remains optional, it would be beneficial and allow us to have a little more control over our data. I know that in the meantime, solutions already exist, with third-party services such as zerobin etc... or PGP (which too few users on the forum use), but such an option would make things easier and would be more "beginners friendly" IMO.
I don't know if it's feasible, and how much work it would be though.