We've had a lot of vendors, like Firebase, approach us at Poll Everywhere over the years. Despite how awesome they are as people, a company, and the huge problems they solve, I've always avoided it getting in bed with any vendor for something that I think is fundamental to a realtime web application. As a result, we developed our own realtime web framework at http://firehose.io, open sourced it under the MIT license, and made ourselves immune to these circumstances.