As a rather illustrative case study look at the history of XMPP at Facebook and Google (Talk). Facebook messaging used XMPP until 2015, but it was not federated - but at least you could use client of your own choice. Then they switched to a proprietary API. Google talk used federated XMPP for years, but then dropped server-to-server encryption, effectively cutting off majority of servers, and then dropped Talk in favour of proprietary Hangouts altogether. So the trend is just the opposite - if the player grows big enough and the community becomes self sustained, they will start walling the garden.