I think the idea is that only the big platforms have to offer a protocol for interoperability You could always disable that in matrix or chat with someone on another chat protocol unencrypted.
But the real advantage is that someone on those big chat apps can just switch to a different (more secure) app without loosing his contacts. Basically this should be a huge boost for open source and trustworthy messaging apps. At least from what I’ve read here:
No clue but maybe you confused it with this one?
https://www.privacytools.io