It feels almost silly to post this as an announcement but maybe others find it useful as well.
I created a little repository GitHub - cideM/visual-studio-code-insiders-nix: The latest Visual Studio Code Insiders build updated daily where a GitHub action retrieves the most recent URL and sha256 for the Insiders build of Visual Studio Code. It supports the same platforms and architectures as the VSC package in Nixpkgs. I currently use this in my own dotfiles on NixOS and M1 and Intel Darwin.