There’s definitely valid arguments here, but I think long-term it would be better to have something like IPFS seeding combined with a smarter nix-store that works with deduplicated blocks instead of with nar files.
I’m confident that this would result in a severalfold reduction in stored size and bandwidth, and hosting doesn’t even need to happen in the cloud (like with bittorrent).
(note that due to the store path hashes, lots of duplicate blocks aren’t detected by sliding window dedupers. So the store paths need to be removed entirely (so variable length doesn’t matter) from the files before deduplicating, and restored after reduplication. See here for more.)