I’m glad to hear some interest on that subject!
Actually we think about it since some time ago, but the efforts were focused on some other issues before coming to this.
There is a PR  which is a first step towards a way to provide new firmwares and boot them after some verification.
Since it’s a delicate topic, we want to advance step by step being careful on the way the firmwares are booted and also distributed, which implies huge security issues, both on server and end device side.
I’m managing such efforts, and will update regularly our wiki  dedicated to this subject.
Thanks for your interest and don’t hesitate to push your ideas and comments either here or on the PR.
 https://github.com/RIOT-OS/RIOT/pull/6450  https://github.com/RIOT-OS/RIOT/wiki/Over-the-Air-Updates-(OTATF)