Matrix does not require a centralized identity server (which exists only for optionally discovering users on Matrix based on their email/phone numbers).
The linked gist is loudly complaining (amongst other things) that Riot's default config points at a centralised one by default.
We've already fixed this (https://github.com/vector-im/riot-web/issues/10553) by simply removing the concept of default identity servers entirely and instead prompting the user to select on demand whichever one they want to use, if they actually try to look up a user based on email/phone. It should be released in Riot 1.4 (on Web, and equivalent ones on mobile etc) in the coming weeks.