Bullshit. the identity server has only one reference implementation. you can run your own but "This won't be very useful right now, though, and we don't recommend it." according to the faq. to date, matrix has no idea how to federate identity.
"The precise architecture of identity servers is currently in flux and subject to change as we work to fully decentralise them."
really? after six years theres no progress on it? matrix handles 9 million users but the web store hoodies and stickers were somehow a bigger priority.