In order to scale the user base of Zwift the Android platform should be the way to go since the entry-level (in terms of pricing) is relatively low compared to iOS devices (and also since Android-based phones start outperforming iOS devices).
This becomes even more interesting with DayDream where Google is building up a low-cost phone-based VR environment which would be a perfect incentive for launching - switching over from desktop-based - Zwift on Android.