The other option for multi-room sync is AirPlay, on any device where that is possible (including wiim), so it’s pretty easy to solve multi-room audio these days.
Chromecast Audio lost the ability to do multi-room sync in a patent dispute with sonos
Unfortunately the wiim mini doesn't support the google cast ecosystem, only the more expensive devices. But the more expensive devices don't support airplay, which seems like an odd choice.
Conjecture on the wiim forums is that they ran into licensing issues so their two flagship products (Amp Pro and Ultra) don't have airplay, but weirdly all of their lower-end devices (Mini, Pro, Pro Plus) do.
The other option for multi-room sync is AirPlay, on any device where that is possible (including wiim), so it’s pretty easy to solve multi-room audio these days.
Chromecast Audio lost the ability to do multi-room sync in a patent dispute with sonos