Ohh, I've been wanting something like that since forever!! The way I have things set up right now is I have a nix flake deploy NixOS LXCs to a vanilla Proxmox deploy, so this could help integrate things a bit more tidily. Plus, of course, declarative networking/storage configuration and whatnot. I'll definitely give this a go sometime.

I haven't used either, but at a glance devenv claims to use Nix while devbox explicitly says it doesn't. I've been happily using flakes with nix-direnv myself and I have no complaints but options are always nice so I'll keep an eye on this!