One crazy thought here, given Zig’s (and the ZFS’s) inclinations, would be to leverage some sort of peer to peer network and push the decentralization even further. As long as you can bootstrap a minimal thing, you could “ask around” your peers for current versions of the tooling and download those from the peers to your machine. Something similar might work for packages, and even a package index that “emerges” from your peers.
Again, just a crazy thought.