Why is it monumental? Java runs on windows already and they are third parties like Bluestacks who have demonstrated running android apps on Windows.

Java runs on Windows, but not Windows Phone, which would be the main target of Android app functionality.

Windows Phone isn't a distinct product anymore with the launch of Windows 10, is it?

No, with Windows 10 they should have this ability

It wouldn't have been so monumental if instead of locking everything into Direct3D they'd used OpenGL instead. Here their own lock-in mentality will eventually bite them hard. If MS will outgrow their dinosaur lock-in approach, they can start supporting GL-Next on all of their platforms when it will come out.

When all you have is a hammer, everything starts to look like a nail.

Windows runs OpenGL just fine (look at anything iD Software puts out). It doesn't run Google's custom Java VM, it doesn't offer AOSP APIs and it doesn't offer Google Play Services. THOSE are the obstacles to running Android apps on Windows, not your obsession with OpenGL vs DirectX.

Is there OpenGL on their mobile platforms? It can run just fine in theory there, but it's not available. Applications are not limited to Java, and often rely on the graphics system a lot and there can be as well native code.

Very few mobile apps need OpenGL. The larger problem is the lack of Android APIs.

Mobile games do. And if you want to translate it into a broader context, what about having OpenGL on Xbox? Didn't MS want to unify their OSes across different devices? So it's really all related.

Last I checked, MS wasn't having problems persuading people to make games for the XBox.

In fact, if Windows Phone ever got decent market share they'd be in a great place for gaming, if they made Xbox -> WP ports easy.

This wasn't about persuading, but about them not being jerks and making life easier for those who develop cross platform applications like games. I'm sure many developers would appreciate using portable API.