What happens if you multitask, say have OMP and browser opened? You'd then need to have Qt4 for OMP loaded and Qt5 for browser.

My real concern with qt5 was how well supported it is on Maemo. I don't see a great deal of apps using it, if any. If you compare the amount of code ripped out in the recent qt5 commit in embedlite, the new port seems to be much easier to work with for some interactions. However that simplification must at times come at a cost of increasing qt library size.