Short: fwupd users download small but in total too much metadata over the internet.
A solution for local distribution is needed. IPFS is too slow, Bittorrent is immediately suspicious on many Networks.
Passim is a new protocol for this purpose, users can opt out, it is secure and the metadata is hashed, and the hashes still downloaded over the internet for verification.
For people who prefer to read: https://fedoraproject.org/wiki/Changes/Passim_P2P_Metadata