But the very idea of sharing my uplink is anathema. Maybe if everyone curated their own whitelists. But once people rely on whitelists from "trusted" peers, all bets are off.

A safer alternative would have users sharing access to each others VPN service connections. That would at least insulate users somewhat from malicious/illegal traffic routed through them.

Indeed, I routinely route traffic through nested chains of 3-5 VPN services. A common criticism is the cost of multiple accounts. And I typically have even more accounts at any given time, for variety.

But if a bunch of people pooled access to their VPN services, or to VPNs that they ran privately on anonymously leased VPS, each one could have a much larger variety of VPN paths and exit IPs. And you could multiplex and split traffic through the VPN network, to increase anonymity. Or aggregate links, using MPTCP, to increase throughput. And you could even implement something like Tor's process of switching circuits every 10 minutes.

I bet that I could implement a simple version of that with routing tables and iptables rules. And some shell scripts. Perhaps with network namespaces, for a little more security. Even Docker, maybe.

But not just sharing ISP uplinks. That will end in tears.

That's not a bad idea, actually. Who maintains those whitelists and how do they get updated? If you want to make the web somewhat usable for others, is it enough to whitelist "google.com"/"youtube.com" only (for example)?