Apparently the main #xz maintainer, Lasse Collin (Larhzu), who was assumed to have simply been offline for the past 24 hours, has now started working on a post-mortem overview page of the incident.
https://tukaani.org/xz-backdoor/
> This page is short for now but it will get updated as I learn more about the incident. Most likely it will be during the first week of April 2024.