I think it was released in scanned form from a printed document (or maybe that was 8080 BASIC), this is the first I've seen in digital text form.

Ok, so the scanned version was indeed 8080 BASIC. However, the 6502 source has been available unofficially since at least 2015. https://www.pagetable.com/?p=774

Nice to see it out there under the MIT license, certainly. This makes it legal to actually use in many scenarios where it wouldn't be legal to use it previously.