Another idea is to use NNTP with email subscriptions (do any NNTP server software have email subscriptions?) and propagations to other NNTP servers as well as SMTP. It is possible to cancel a article, but some servers (and clients) may ignore the cancel. You can still distribute the messages in many other ways too (does not have to be limited to internet), including but not limited to email and NNTP. Maybe also IPFS.

Another consideration is Fossil. Fossil artifacts are identified by a SHA1 hash or SHA3-256 hash, so you can make a magnet URI involving it. SHA1 hashes are listed in the Wikipedia article for magnet URIs; SHA3-256 isn't, although it would still be possible to do (perhaps "urn:sha3-256"). Fossil also includes a HTTP server (or can run on an existing HTTP(S) server), which the artifacts can be downloaded from. Some Fossil artifacts are structural artifacts; if it is a manifest of a check-in then its data will list the name and hash of each file. (I do not know how Git and Mercurial work; I do not know about how the similar things would work with Git/Mercurial, if any.)