The Surface Duo looks like a very cool device that I would probably never use over a phone with one good screen, more power and a great camera. Similar to tablets, I personally just reach for the phone or the laptop or my TV, and never a tablet.
But a Duo released with some more power and some imaginative use cases might start to sell. I think it's a shame that the larger Neo and Windows 10X seem to be dead before arrival, because it might have led to something interesting. But Microsoft has not resolved the conflict between Windows for everyone, and an application store that feels competitive and properly populated, so locked down devices have consistently failed for them.
The Duo running Android doesn't have that limitation, so the bigger question might be if Microsoft can do a sufficiently sophisticated job customizing Android, making it feel like something more than just Android, and making it work perfectly with this unique form factor. But it's hard to see the business case for all the resources going into what still feels like a very niche device category.