For mobile developers, the biggest difference is that they'd be using the Qt framework instead of the Android framework.
So the pitch at least for mobile developers, should be why it's a more pleasant and better (and more productive) experience to develop mobile apps with Qt vs the Android frameworks.
I'm not how much better Qt is going to be since I haven't used it. But I've been a long-time desktop Linux KDE user, and one of the biggest gripes I have with KDE is that its quite unstable and buggy compared to Mac and Windows.
KDE 4 became almost very-stable with 4.13+, but the early version of KDE 4 were horribly unstable. With Plasma 5, from what I hear, things got worse again.
This is the biggest problem, I think. To the people who have actually used KDE on deskotp Linux for a long time, how many of you have enough confidence in the stability and reliability of a mobile Qt/KDE environment to use it everyday?