If they are smart about it, it should not be an issue. I don't understand why Windows Phone is not doing better considering its a C# implementation. Windows Phone should have a .NET framework built into it so it should be easy to take a Java or Visual Basic app and bring it into Windows Phone.
If HTC does similar and makes it easy to import Java, Visual Basic, and C#. There should be no reason for the OS to be useful.
The only problem is if Google or Apple used processes that are specific for iOS or Android which I suspect to be the case. There really should not be an issue of implementing another languages programs into Windows Phone unless Google or Apple artificially block them by the way they give access to the graphics, sound, and touch inputs.