Hm, even when there are 10 different server implementations (or the ~50 client implementations there are today), we’d hope they would align to the same spec - just as with HTTP, SMTP, TCP/IP etc. There’s room for experimentation without introducing fragmentation, and any useful experiments would hopefully rapidly get merged into the spec. And if they don’t then yes, you risk a fork on that particular feature (the equivalent of only Exchange supporting email recalls, or browser vendor extensions), but it’s not the end of the world.