What do we mean when we say "screen" and what do we mean when we say "display"? What's our definition of the terms "screen" and "display" used here? What's the relationship between them? I find it strange to have both screen.displayFoo and screen.Foo. screen.displayChanged?
Drop the term "display". Stick with "screen".
"Screen dimensions in its native, non-rotated (rotation = 0), orientation"
I find it misleading for screen.width and screen.height to be the rotated dimensions since the screen itself doesn't resize when rotated. Who rotates is the content of Window element. Window element is the one providing the feature of actually rotating the GUI. Having that said, I wonder what's the dividing line between Screen and Window. Which is responsible for or provides what? How come we set the orientation in Screen if the GUI rotation will be actually done by Window? I think allowedOrientations should stay in Window. Window and Screen can have diverging orientations. Screen.orientation is the orientation where the system is (physical orientation + big pack of rules and policies), whereas Window.orientation is the actual orientation of the application's GUI. Window.orientation follows Screen.orientation according to his Window.allowedOrientations.
The prefix "current" is redundant.
Property is already inside screen, thus no need to repeat ourselves. It also looks inconsistent when put side-by-side with Density. Either both have the "Display" prefix or none of them has it (the latter being what I prefer).
When making API proposals I think it's helpful to include proper/"real" documentation (for methods, enum, etc) in it. That will help clarifying/validating the meaningfulness of the chosen nomenclature, etc. What are the units of width and height? Pixels?
By the way, current implementation of mdeclarativescreen assumes that a non-rotated screen (angle == 0) is always in a landscape orientation. That doesn't hold if the native aspect ratio of the screen/display is portrait. We just fixed that in libmeegotouch
It's good to keep that in mind.
Hope that what I said makes sense since I haven't spend much time in this project (could have misunderstood some concepts).