I'm sure that's where it started, but it's perfectly usable from userspace; https://liliputing.com/nestbox-makes-running-linux-virtual-m...

They have something called microdroid which is a special VM which runs special android apps: https://source.android.com/docs/core/virtualization/writeavf...

Of course, running a custom VM image like crostini would require system level support but that doesn't seem like it would be a problem or outside the scope of the avf architecture.