It's not quite what you describe, but Ivan Vučica is currently working on a GSoC project to implement a subset of UIKit with parts of Quartz and CoreAnimation in GNUstep.
"This proposal covers implementing a flexible animation API compatible with a certain popular existing desktop and mobile platform, as well as adding APIs compatible with a popular mobile platform. This will allow extremely user-friendly interfaces, as well as allow development or porting of applications that use CoreAnimation or UIKit API on platforms that don't yet support it."
http://www.gnustep.org/