But there is one problem with that strategy: if Microsoft would support running Android apps on Windows Phone, there would be little incentive left to write native WP apps. Everybody would only write for Android, making it hard to differentiate the platform.
I wonder if it would be feasible to support Java and maybe some (most? some well-defined base of?) Android APIs in "native" Windows apps, in a similar way to how JavaScript and HTML are supported via WinRT's notion of language projections. Although this would mean narrowing the goal from "making Android apps run on Windows" to "making Android apps easier to port to and maintain on Windows".
But there is one problem with that strategy: if Microsoft would support running Android apps on Windows Phone, there would be little incentive left to write native WP apps. Everybody would only write for Android, making it hard to differentiate the platform.