Retaining copyright isn't what matters. The license they choose on the copyright they (naturally) retain does. It is possible that they could craft a license s

Retaining copyright isn't what matters. The license they choose on the copyright they (naturally) retain does. It is possible that they could craft a license such that protocol-incompatible changes are not allowed, but I don't think that would be in their best interest. This is a starting point. The risk isn't fragmentation, it's crickets (ie nobody cares) and an untested protocol that may need multiple versions to get right.