32.  Although technically, the 32 limit is per Sonos system, but you can have more than one Sonos system on the same wireless network.  So you could resolve your issue by setting up 2 systems in your home.  If there are different areas in the home that you would never really want to group together, that could work.  Say for example you have guest room that do not need to be played in sync with the main living areas.

There is a limit of 32 devices per Sonos System, although you can have multiple systems per Wireless network..