FWIW, I've been running Synapse since 0.20 or so (for at least 2 years now), and there has never been a breaking change in the protocol as far as I'm aware. I had to read release notes at some points to get the upgrade to work, but it was mostly Python-library-related stuff IIRC.
After Synapse 1.0 is released (sometimes next month, IIRC), I'm definitely deploying my own homeserver, and federating it with the rest of the world.