I don't think I'd be the person to ask. My impression would be you would need to port the entire Android runtime and have all the available APIs for apps, have full support for all of the hardware supported devices use and more. For virtualization a hypervisor would need to be built if an existing solution doesn't work out. There's probably a lot more I'm missing. Exiting Linux is an extremely far future wish and I think the team would prefer these projects to mature first. I'm also not a microkernel developer so there's countless details I think I would likely be missing out...

I'd be more interested to see a deliverable high-security daily driver desktop operating system with a microkernel with app sandboxing, permission controls, exploit mitigations etc.

Disposable VMs would be something the project would look at when making a VM manager. Running apps in GrapheneOS VMs would be part of that idea.