Short: fwupd users download small but in total too much metadata over the internet. This is a beginning of something important, and the tech can be used for local updates and a lot more.
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.
To 3 I suppose one would disable p2p download and only enable seeding/sending the stuff