For now it will be a different coding environment for each platform. They will look and feel similar.
The main reason for two platforms is that Android and iOS have features that are unique to them and if we were to create a platform that was “code once/deploy on multiple platforms” we would only be able to offer features that are present on both platforms. Given that there are many features that are only available in each platform (eg. near field communication and material design on android, force touch and human interface guidelines on iOS and many many others), if we wanted to allow continued high end flexibility, rather than reducing to the lowest common denominator of features available on both platforms, we have to keep it as two separate platforms.
That being said, this is just the way we are planning to start out, but in the future, we would love to merge them as much as we can to make it as seamless an experience for all Thunkers.