Bringing Android app support to the platform would kill most developer incentive for developing native WP apps. That in turn would more or less mark the death of the platform. At least I wouldn't see any point in sticking with WP when even MS has given up. I'd go back to iOS full time. If I wanted to run Android apps, I'd buy an Android device.
Why do developers adopt WP? Because they want to make money selling their apps in the store, or with in app purchases, or showing ads. They want access to the WP user base that is close to 50 million people worldwide.
If WP could run Android apps, developers would have a path with lower costs to reach that mass of users, but also with lower revenues. The user experience of the Android apps in WP is inferior, that means less usage and less revenue. So, both variables are reduced and produce mixed results for different developers. Some developers would benefit reusing their Android app, for other developers is a bad strategy because the loss of revenues is bigger than the cost savings.
Let's classify developers in three groups:
1)Developers for whom the cost of a native WP app is much higher than the revenues they could get from the store. So, those apps won't come to WP any time soon. The Android strategy is a WIN-WIN situation. Devs earn money reusing their Android app, and wp users have access to apps that would be impossible to get in native form.
2)Developers that don't make much money with their wp app, or developers that are planning a WP app which is just becoming profitable with the growth of the user base. For them the cost of development is relatively important, the savings of reusing the Android app could be higher than the loss of revenue of an inferior user experience. So, some developers would remove the native wp app (probably no a high quality app) and would submit an Android app. Some developers planning or in the firsts stages of development of a native app would cancel their projects to submit an Android apps. This is the big fear of some WP fans.
3)Developers that get good revenues from their native wp apps, for them the cost of development is less relevant and the loss of revenue caused a low quality app is bigger, so they would continue with native apps.
The bottom line is not bad:
-The Android strategy would give us access to several thousands small apps that aren't economically viable in WP.
-We would lose some native apps from the store (probably low quality apps anyways, the android apps could be even better) and some native apps in early stage of development would be canceled in favor of Android apps.
-Nothing change for the developers of top apps, they would continue with their native development.
But the situation can be improved if:
-Microsoft rejects any Android app coming from the group 3, top apps. Some devs or companies could chose a wrong strategy due to lack of knowledge, bad management, or an irrational intention to simplify things. The Windows store has to be selective.
-Microsoft has to subsidize developers of the group 2 to promote native development. This subsidy could be a bigger share of the revenue from the store, technical assistance, money payments, more exposure in the store.
-Microsoft has to increase the adoption of WP, because as the user base grows more developers move from the group 2 to the group 3, and the group 3 is not interested in submitting an Android app.
It's interesting that the Android strategy is more beneficial and less risky as the wp user base grows.
Lets say that WP reach a 10% of market share of the sales, It would be needed a couple of years to reach a 10% of market share of user base (which is the important variable for devs). Even with a 10% of the user base there are several thousand of apps that aren't economically viable in that level so Android apps could help to fill the holes. And with 10% of the user base there is less risk of destroying the platform accepting Android apps, because the group 3 is bigger and the users are guaranteed to spend a bigger percentage of their time with native apps, 80%-90% of the time?.
The ideal scenario would be to start working today in the implementation of the Android SDK to be released with Windows 9, and reach 10% of market share before that thanks to the improvements of the platform and an really aggressive price strategy.