I've experimented around with HA and some other options for my home. We bought our home just a few years ago, and not likely to move soon, but I thought about perhaps registering an email for the house, and using that for accounts that I wouldn't consider taking with me. Selling the house would consist of clearing out most (perhaps all) email from the inbox, clearing the trash, changing the password for the email account and then handing it over to the new owner. Then they just have to go through the 'forgot password' routine to create new passwords for accounts linked to it. Anything I plan to take with me would need to be disassociated from that account first, of course.

This is just a thought at this point, frankly, so there are obviously some gaps that need to be worked out.