[RussianCow]

At the very least, you could reuse model code and some (most?) business logic, and likely the data layer as well. Even if you don't reuse any UI code (which seems unlikely), that's still significant.

Edit: In the long run, though, this type of approach opens up the opportunity to abstract low-level differences between platforms in a way that still uses native UI/functionality under the hood. For instance, you could make your high-level components generic enough to be used on any platform, and only change the implementation details per platform. You can do the same with plenty of other APIs as well (local data storage, location, etc).