Does anyone know if PC and Mac players can play together?
PC & Mac, yes.
But cross-platform kind of suggests mobile devices and consoles would be supported by this new update, which I'm not very sure about, but from what I've read, doesn't seem likely.
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It's likely as long as the device has WebRTC support, which I believe Chrome for Android does have
Data is Data is Data is data. As long as the software can read the protocol of messages the OS or hardware doesn't matter.
I never understand why this question needs to be asked.
As long as the OS/device will support WebRTC in the upcoming MP. Then it's all fine.
of course they can, but it will require both computers being connected to internet and you designing a websocket server or similiar. etc etc etc
The new multiplayer plugin comming out will also allow this as the connection between players will be done via the browser itself. As long as both computers are running i.e chrome it will be fine.
Yes, it's supported by Chrome and Firefox on any platform, including Windows, Mac, Linux and Android. (Except Chrome for iOS, which is really a different UI over Safari.) Hopefully support will be coming to other browsers soon.