I've been thinking a lot about how the SDKs tend to not fully support a protocol version, and ways to let different language SDK client-server interactions do version negotiation despite one missing the latest version of a single capability, for example, and the idea that it shouldn't stop them from using the latest for everything, but using the previous protocol version for just that capability...

...or maybe some big things are bundled in a "base capabilities" category that represents spec version support, while the rest of capabilities' versions can be negotiated separately during the initialization exchange.

I also want to float the idea of Session/Sessionless & Transport being capabilities with introduction as such via capability versioning.

I think this could bring more modularity, instant value to prioritized implementations/updates, and a better user experience especially in the first few years of this protocol.