Once you start gluing various ported Linux applications onto these alternative OSes, they start to lose their distinctiveness and raison d'être. If you are using Qt/KDE apps, anyways, what does Haiku really bring to the table other than a smaller footprint?

I never programmed for BeOS back in the day, but my understanding was that half the advantage of it was its consistent clean ground-up API for building multimedia applications. I'm not sure how well that has aged, tho...