What about a roommate situation? I mean, you share the same house for your whole account. Then maybe have it where you can access your other chars storage, or at least maybe the main bank stash or something, for easy transferring of stuff without having to log out. Or even a much bigger transfer stash, that can be upgraded like the bank. Maybe storage mules don't fit into your grand scheme for the game, but I would say that most people that have played a decent amount use them. It would be a nice house perk that wouldn't take away from the main world, like a private garden or craft station would.

Or even have it so your other chars are actually in the house, like npcs. And have it where you can actually become one of your other chars there. Maybe a menu pops up as you leave the house asking which char you want to be, and that's the char that re-enters the world. No idea how hard any of these things would be to code, or if they are even possible, but with new races coming alting will be even more prevalant. And anything that keeps a player from having to fully log out to switch chars is going to be nice.