Nobody but designers who think too highly of themselves wants this. Everyone else wants the app to fit in with the platforms toolkit. This requires the designs to be different.
"Writing two pixel+cultural perfect apps on two platforms, keeping them in sync, making sure they're not buggy, attempting to share code, attempting to keep them both secure is incredibly expensive. If you don't believe me then do it yourself."
Which is why I don't do it the way you described. I embrace what makes each platform unique.