For what it's worth, recent versions of IE are already evergreen and auto-update by default.

The real culprit behind us still having to support IE8 for some clients is your average enterprise IT department. They'll find ways to lock down updates on any browser. Just as some IT departments have auto updates locked down on Chrome/Firefox already, they'll probably demand a way to do that with Microsoft's browsers too (or find a way to block the updates without Microsoft's support).