Or the reverse, most people have specific IPs that they'd like to route traffic through the VPN but mostly don't care about the rest.

Again, you wind up creating a huge list of exact IPs and creating the routing rules is a PITA.

I don't understand. Having a specific list of IPs they want to route over Wireguard is the one that is easy today. It's the inverse (everything except these IPs) that's hard.