I very much like the idea of a uniform algorithm for this - similarly to https://indieweb.org/post-type-discovery. During that session the list on https://spdx.org/licenses/ came up as a source for licence indication - unfortunately neither rel="licence" nor microformats seem to be offering a way to indicate a machine readable licence indicator yet. It might be beneficial to include a proposition for that along with the algorithm.
(Oh, by the way: this entry was written by Peter Molnar, and originally posted on petermolnar dot net.)
Responses from the internet
https://quickthoughts.jgregorymcverry.com/2019/02/11/you-dont-see-parsers-picking-up-relquotlicensequot