[exe.dev cofounder here] Thanks for the feedback! We do not support private registries yet but it is very much on our mind, it is one of the first things business customers ask for so we know we have to build it.

We are also exploring alternatives for pre-configuring your VM. (Because we make lots of VMs and feel this too, so it is very much on our mind.) One is a sub-second VM "clone" feature, so you can configure a base VM to use as an image.