As I'm working on a signing scheme for release authentication, this is a welcome news.
To alleviate the issue of mutable releases I had set up a mirror of releases checksums to be able to detect releases alterations. This is not needed anymore for immutable releases.
And automatically publishing checking of releases artifacts is also a good recent change by GH: in that project mentioned above I have developed a cli downloader checking the checksums of the downloaded file [1], but to be useful, it required the project to publish checksums, and the project to be mirrored. Now both of these requirements are dropped and the tool is readily useful for all GitHub immutable releases.