I read Paul Thurrott's article regarding Android apps on Windows Phone prior to the announcement and I got rather disappointed myself about the future of the platform. But what was announced was very different from what Paul had predicted, and not what Blackberry did...build a runtime to run Android apps on the Blackberry platform. It may not seem like a big difference, but the implications are vastly different.
Blackberry decided to basically emulate Android on their devices. In theory, this would open many apps to Blackberry handsets in cases where developers had not written BB apps. It seems like a good plan. Except in practice, it allows developers to be lazy, thinking "why would I write a Blackberry app if it will run the Android version?" So, BB app development suffered. The other side of that story is the fact that many Android apps don't work properly on Blackberry because of an important fragmentation issue on Android. There is the open source Android Open Source Project, AOSP, which entails all of the APIs needed to write apps that will run on Android. But, if the app is in the Google play store, chances are good that it doesn't use only the open source Android APIs, it uses proprietary, closed-source Google APIs. And these APIs are prohibited from being emulated on Blackberry, so many "Android" apps can't run, or cannot run well on Blackberry devices.
Microsoft has chosen a different method. This allows a person who is writing an iOS or Android app to easily convert the app to Windows and Windows Phone. This isn't emulation on the phone, this is a tool that assists a developer in making an app that is written in a language that they aren't used to programming with. This will allow a small app developer, with little or no experience at writing an app for Windows to take their existing app and turn it into an app that is native to Windows devices.
I think this will potentially help bring a lot of missing apps to the Windows ecosystem. You do mention a good point in your post, however. There are certain apps, like Snapchat, who are actively shunning Windows as a platform. You are right that this is an entirely political, and not technical, decision. And a decision like that cannot be fixed by creating an easier method to creating Windows apps...but, it could get the ball rolling. If bank apps start coming to Windows devices due to ease of app development, people may have less reason to avoid Windows, and choose a Windows powered phone if they get fed up with their existing phone. Enough people do that, and market share may reach some arbitrary number that is hard to ignore, even for a hard headed group like Snapchat or Google.
Crazier things have happened.