Rene has set out the current position as I understand it. Synchronisation of zones is a very important capability if Roon is to challenge Sonos. Of course, Sonos has proprietary hardware and a single protocol. Roon is aiming higher than that.
Synchronisation of RAAT zones (RoonReady and RoonBridge devices) has few users now, but after 1.2 and as more devices get released, it will grow. I believe it will eventually outgrow AirPlay, Squeezebox and Meridian streaming and those protocols will be regarded as legacy systems. RAAT let’s the DAC own the clock.
But having shown how to do it right, it would be interesting to hear from @brian what the prospects are for synchro across those families. If anyone can do it my money would be on him.