If you build your game using NWJS, then yes you can have a multiplayer game to upload on Steam since NWJS uses WebRTC. Steam won't be handling all of your multiplayer though, as the multiplayer object is technically Peer to Peer.
WiiU browser doesn't support WebRTC, so no..
Xbox One - No, at least not yet..
Once Microsoft Edge gets DataChannels and PeerConnection API fully support, then you will have multiplayer support on Xbox One.