Kitty's standard is described for other people to implement both emulators and clients for. Since this relationship already exists, there's enough friction between emulators implementing new features, and clients actually using them (in a backwards-incompatible way), that I believe one can be relatively sure their emulator will support clients well into the future.

Either way, I agree that kitty's protocol should become a versioned standard, but I also don't think that people will be very quick to change it at this point.