We estimate that by 2025, Signal will require approximately $50 million dollars a year to operate—and this is very lean compared to other popular messaging apps that don’t respect your privacy.
If you read between the lines, Matrix 2 is practically about handing the client state over to the server (what they refer to as “sliding sync”). Realistically, this is an admission that the protocol is too complex to be handled efficiently on the user’s devices. I’m not saying there are not clear benefits (and new trade-offs) to the approach, just that in the grand scheme of things the complexity is shifted elsewhere (and admins foot a larger bill).