It seems to me at least as likely to have the "Win-OS/2 effect" of putting a bunch of apps (most of which feel really out of place and none of which feel great) on the platform while causing even fewer developers to target it natively because, hey, why not just invest all the extra effort a native version would take into the Android version since it "runs" on both platforms?

Edit: Which isn't necessarily to say that wouldn't be Microsoft's best option for Windows Phone right now. Especially since games and entertainment apps are such a big part of the app market and their "nativeness" tends to be less important.