In answer to the Windows Phone question, Systrom said that "Windows Phone is a really interesting technology. It's an up and coming OS. They've been doing really well. We don't have anything to announce right now, but we've talked to them about their platform and we're learning," reported by Tech Radar.
I think the moment where Instagram could have made a notable difference to the story of Windows Phone has now passed (I'm open to discussing that point in the comments below), but a release would still play an important part - not only would it legitimise Windows Phone in the eyes of many, but it would demonstrate to others that Windows Phone is as capable as the next mobile OS in handling third party web based services.
Technically there doesn't seem to be much in the way that would make Windows Phone a bad platform - there are countless apps out there that can replicate the basic editing and image filters that Instagram uses, while integrating with social networks is one of the key advantages throughout the Windows Phone UI. I can't imagine that 'upload image to server with some metadata' is too hard to do.
So what is Systrom and Instagram "learning" about Windows Phone, and when will they decide they have had enough of a Windows Phone education to join in the fun?
Given that Instagram is now owned by Facebook, perhaps Microsoft just needs to approach this in the same way as the WP Facebook client, and code it for Instagram in a sweetheart deal?