I think your second sentence may not be write. What if that person (X) is currently in a 1.0/1.0a licence agreement with Y, and Y becomes a party to v 1.1? Y appears now to have inconsistent contractual obligations - they have promised WotC to renounce 1.0/1.0a, but have promised X to honour it.
If your license obligations are inconsistent, that means you have violated one or the other, and lose the rights provided by the one you've violated.
So, say I have a D&D 5e ogl supplement I've created, and a Mutants and Masterminds supplement. If I decide to make a OneD&D supplement under v1.1... if Green Ronin doesn't also go v1.1, maybe I lose the right to sell/publish that M&M supplement.