Really good timeline of what is known to have happened so far. It looks like the rogue developer deliberately introduced a vulnerability in other package, too - I haven’t seen anybody else mention this.
Reading the dev’s GitHub history, they’ve been making changes to other open source projects too around compression. It also appears they/somebody involved has other accounts, too.
https://boehs.org/node/everything-i-know-about-the-xz-backdoor