This is the stupidest thing I’ve ever heard, but I have no doubt that it is true. Microsoft is just stupid. Dual-booting does not solve the underlying problem that Windows Phone isn’t very compelling for consumers.
If you offer somebody choice between Windows Phone and Android on boot, they are going to (perhaps foolishly) pick Android. Dual-booting doesn’t help Microsoft one bit.
Microsoft have already played their trump card, acquiring Nokia. They need to go all in on it, or they are going to lose. They need to reallocate all of the resources tied up in organising manufacturer relationships and focus on building a first-party product.