Our countermeasure is that in Matrix you can’t build gatekeepers, as conversations replicate between the participating servers. You can’t talk to someone on another server without literally sharing ownership of that conversation with them. Now everyone could chose to congregate on a single server (e.g. matrix.org has about 35% of the users on Matrix right now, given it’s the default) but there is no advantage to doing so.

Meanwhile we’re building out P2P Matrix to avoid being dependent in servers altogether: arewep2pyet.com