Here's my thoughts, not to be interpreted as suggestions for you.
Apples driving me away from my much loved iOS simply because they refuse to make a small increase in the size of the phone to accomodate what has become standard size displays in most smartphones.
Deeply invested in iOS apps & the like, I too had the same concern you do. Then I changed my mind thinking yes, I do have an iOS investment, yet I've gotten my money's worth & I don't want to attempt to have a mirror image of my Apps on a fresh new platform anyway.
I want _some_ of the essential ones, the rest can be unique to Windows Phone. For example their will be Dropbox, Evernote and others. Then for those that don't port to Windows Phone right away, I'm sure there will be suitable alternatives.
So that's my plan. Buy a nice Windows Phone, use it, learn something fresh & new in the process.
Now I'm in a great position. If I really like WP I'll migrate to it completely, if Apple wakes up next year or the following & includes a modern display I will return, or I may find the SGS III I'm currently enjoying to continue to be the favorite it is today.
There's nothing like choices. 🙂