There have been a few attempts at "universal" UI frameworks that let you simulate a small subset of features on desktop and pythonista. search forums for unipage, which is Kivy based. There was also an attempt by someone to create a dummy pythonista UI module that interfaced to tkintker or some other framework.
In both cases you end up with a very limited Subset if the full feature set, since it is difficult if not impossible to capture all of the subtleties of native code, and differences in interface. I think someone also has posted examples of a web based (flask/js) approach that would be near universal, but doesn't really lend itself to easy development in the iPad.
What might be better is to try to write your code such that the backend logic is standalone, not relying on any UI. Then write your user interface code such that it checks platform, and presents using the appropriate native library. Easier said than done.