But that would be like what we have today when an application is not properly hildonized, like the menu would be horizontally arranged and take screen real estate all the time, even if not in use. - Right?

That's not what i meant by "port", that would be running it without (much of a) change.

By "port" i meant integrating the application into the overall look&feel of the target platform. That's gonna be tough with applications like Xchat or Pidgin. (A quick guess would be it's not gonna be tough, but completely impossible without a complete re-write...)