But this does not “cancel” existing licenses. Instead, what it does is create a hard fork, between 1.1 content and 1.0 content.
Basically… any content released under the 1.1 license is not usable under the 1.0 license.
The statement, in the new license, that the old license is “no longer an authorized license agreement” does not apply to existing licenses anyone may have to 1.0 content. Absent your consent to the 1.1 license, its terms don’t apply to you.
Instead, that language is meant to defeat the forward compatibility clauses in the 1.0 license. Absent that language you could freely use 1.1 content under the 1.0 terms because of the forward compatibility language in 1.0.
This means you can continue to “Use” (as defined in the 1.0 license) any of the content you were using before.
However, it also means if you “Use” any 1.1 licensed content, then either you are in violation of the 1.0 license (and then thus have no rights) or you are subject to the 1.1 license and its terms.
So, this does create some hazard, in that any one using 1.0 content under a 1.0 license needs to ensure they don’t in the future use any 1.1 content.
But if you stick to 1.0 licensed content you are ok.
This can still cause problems. If you are in the business of selling DnD compatible game content, you now suddenly have to make a choice between loosing forward compatibility and having control over your revenue.
It still sucks.
But any content you could sell yesterday you can still sell tomorrow.
The contract has explicit, custom, definitions for several basic elements of contract law. It explicitly declares what consideration exists and what offer and acceptance look like.
The party defining those terms is Wotc. They are bound by something called “promissory estoppel” from representing that those things weren’t present in the original 1.0 license. They cannot revoke your 1.0 license unless you breach the agreement.
They can set a trap for you, that will capture 25% of your revenue, if you end up incorporating 1.1 content into your previously 1.0 derived works.
So, be careful. But they can’t take away what you have now.
It can still also hurt various businesses to loose forward compatibility rights… but anything derived from purely 1.0 content is still 1.0 licensed and they can’t take that away unless you violate the 1.0 license terms somehow.