[ygaels_armpit]

Yes I think any new system would have to see the old one grandfathered (give the current incumbents time to find something useful to do instead of jetting off to conferences all year).

Browsers/OS would be reasonably easy in most circumstances, but there are embedded devices, load-balancing configurations, other esoteric uses for DNS (text records, mail etc) that'd have to be considered as well.

[Senji]

An attack surface is ISPs and Governments strongarming them to use their own DNS roots which can then be plugged into the "new" root servers conforming with the theoretical browser vendor, os vendor alliance.