It barely matters beyond MS' marketing message. Here's why.
Anyone remember BB OS? They enabled Android apps trying to save their OS from death. What happened? The runtime was badly implemented hack. Not only did it not have all the services needed to run average Android apps but it was always lagging behind the Android platform releases which limited any devs to very old versions of the Android platform not allowing them to build interesting, modern apps to the platform.
Making your Android app run on Win10 will not be simply dropping the APK to their store. Firstly, you’ll have to deal with the lack of Google Play Services. You might already be doing that if you distribute your apps in the Amazon store so that might not be a blocker. But even beyond that you will immediately duplicate your QA efforts required for each release. You will also keep maintaining a separate branch for the Windows platform. It’s going to be A LOT of extra work. If I had to guess you’d be better off just building native from effort (and budget) point of view.
Then there’s the big issue. Cross-platform apps SUCK. Each platform has their own UI and UI patterns. Users learn to use (possibly unintuitive) UI controls through platform consistency. What MS is now doing is the destruction of their platform consistency. Firing up an Android app on your Windows device is like getting slap to the face. All new visual, controls, control flows, everything. You don’t want to do this to your customers!
This is a desperate marketing move by MS. They’re trying to get the non-tech crowd to think that this is a good idea (just look what the verge headline is.. ugh..). They will also, no doubt, pour money to devs willing to put time on putting their apps to the store. The result will be that soon there’s tons of partially working apps that will never get updated in their store and they can claim victory.
MS is not the first one to try this and probably won’t be the last. The idea just is fundamentally flawed and will not work no matter how much muscle there’s behind it.
If you want to be on Windows platform but don’t care about learning their platform devving go through the browser. Web is not dead. Build mobile web but keep it in the browser.