What is the official stance, anway?
Is Xonotic a new game, with only limited relation with nexuiz? will it explore new features and ideas? seem so. New animation with different frames will break compatibility, but other than that... I don't see what else may break compatibility... at first.
And breaking compatibility is a bad thing. But doing so "free" the ability to upgrade the protocol and add lots of nice things and ideas. But on the other hand, both games will share the engine. Both will use DarkPlaces engine. And It will be a good idea to continue like that forever, since that way, Xonotic gets for free any enhancement on DarkPlaces.
So is see exciting oportunities that are not really there, and a break of compatibility that is not really needed,... yet, but will be in the future.
The cool thing would be for Nexuiz to die, and Xonotic be just the "continuation" of Nexuiz. I suppose once the war fog clear, It will be visible what this things result. Hell.. both projects can continue, and canivalize each another ideas and features. Like KPDF and Evince, ... Evince started as a fork of KPDF. Now everybody uses Evince has it is sexy and easy to use, KPDF is butt ugly. But Evince can learn from KPDF upgrades and things. It pays to stay "friend" to the old codebase. Is cool to break things to achieve things. But breaking compatibility for the sake of it is very expensive. And maybe is needed, since Xonotic really is taking a interesting position as a reboot of Nexuiz, so breaking things could be part of the "growing pains" we have to expect from this.
I AM CONFUSED!!!