I wish there was a way to automatically nuke the image on shutdown, and then spend 15 minutes to have a script auto-populate a few games in my steam library at next boot. It’d save $5/month, and also solve the OS update problem.
You can use the CLI to create/destroy instances, so what you could do is write a script that has Chocolatey (or boxstarter, which is a bit more for this purpose) install Steam, run it when you login, and then have another script destroy the instance using the cli command.