In earlier versions of the Windows Phone operation system, app support has not been the best, due to the strong grip Android and iOS devices have on the market. With the release of Windows 10 however, which aims to be a cross-platform solution for all Microsoft's devices (PC, consoles, tablets and phones), this might change. Not because Windows Phones will magically gain huge ground in the mobile space, but because they might be able to run emulators for Android and iOS apps.
Most popular apps and games are released for both iOS and Android alike, and if the rumours reported by The Verge are true, Microsoft are looking into ways of making them all work on their phones. This way the library of available apps will increase dramatically, and even if the emulators are dropped Microsoft is still working on software development kits for both iOS and Android developers, to make it as easy as possible to port apps to Windows 10.
You can read about the rumours in more detail here, and no matter what happens we are glad to see Microsoft taking app availability seriously. That would be the key to establishing Windows Phones as a third viable option for modern smartphones.