In my proposal I have linked to a few rendering issues on HiDPI screens, and presented an initial timeline how I plan to fix them.
But I can still shift my proprities, depending on your input! Do you have any rendering problems with KDE applications on a HiDPI screen? Tell me!
Just write a comment to this blog post with your most annoying problems, and chances are good that they’ll get fixed during my GSoC time. If there’s already an open issue on the bug tracker, feel free to link to it. Otherwise, please also state which version of the application you use and what your scale factor (Systemsettings -> Display and Monitor -> Scale Display) is.
I’ll collect those issues on my Summer of Code Status Report page.