If you look at the iOS version, you'll notice that the design is already flat. Due to the app being a port, not a total redesign for WP, I'm trying to design the app so that any shadows, glow, etc won't be present in the WP version. I'm basically going for flat/clean, not metro as metro requires me to use things that just won't work in Haze - Pivots, Accent Colors, App Bars, etc. If MS were to loosen the guidelines that define metro, it would be MUCH easier to move iOS apps over without forgetting metro entirely.
As a designer, I'm more focused on getting the gestures and animations looking as smooth as possible and making sure all of the technologies used to the design the iOS app will work on Windows Phone, and if they are not, find and implement the alternative.
TLDR: Making it metro requires me to rethink everything that made the iOS app great. Doing this would push the release date past the 1st.