Currently we have one customer that really want this and many others that could do with it in a similar way to Bonjour forwarding.
I was playing with things today and though I had found a solution but it only worked for 15 seconds.
I moved one device to a different VLAN - the kitchen Sonos unit which the staff need access to.
After moving this device to that VLAN I was controlling that device on the same subnet (Staff) but when I changed wifi back to "Owner" (where the rest of the Sonos kit sits) and was connected to the "Owner" wifi, I was still streaming from my device to the kitchen and was able to play/pause and volume up/down but this only lasted for 15-30 seconds after which I was only able to see all the other devices and the audio stream stopped.
I thought the solution might be to have at least one Sonos piece of kit on each VLAN and then they would communicate, sadly not the case but I I've proved that the equipment could communicate between the VLANs for a period of time units it probably realised it was in different VLANs.
Please let me know if you would like to test this further!