This is a brilliant product and something that needs to be built.

Gitlab for Intercom.

One feedback though - the whole value here is the product. I would suggest not building your transport at this point and making Pusher/Pubnub/Firebase/Ably pluggable as transport.

99% of your tickets will be "my message wasn't delivered" otherwise and it will take you years to perfect this ...which is something that has been reasonably solved at very cheap cost.