Apple will never fix the lag on the rMBP because it is impossible to do it on the current hardware. I have base 15' 2012 rMBP with a 650M GPU. I have also briefly tested on newer versions of the 15 rMBP and none of them solve the lag issue. HiDPI resolutions with the upscaling and downscaling are really intensive. The animations will never be as smooth as iOS. It is amazing that Apple was able to create HiDPI resolutions with current generation GPUs. However most of it is through deep optimizations through the software side. When people say the current lag can be resolved through software, I disagree. Apple might have made lag worse between Mavericks and Yosemite, but even Mavericks had lag. Apple is going against the limitations of the hardware and facing a massive computation problem has increasing HiDPI resolutions does not scale. Increasing the HiDPI resolutions creates an exponential drop in UI performance. Hence why iPad and Iphone 6 can be buttery smooth 99% of the time and rMBP only 90%; due to HiDPI resolutions which are picked based on the device screen size.. The higher the resolution you go the more intense computing/gpu power you need. The only workaround is to "Reduce transparency" and use a non-HiDPI resolution high enough that it still looks good on the retina screen. Using rdm you can use a resolution of non HiDPI 1900x1200 or 2048x1280. Resetting the p-ram or any other workarounds will not work. Excited to what WWDC brings on the rMBP front. Apple had 3 years where they did not improve the rMBP besides minor updates. I hope they do some custom silicon to handle all the intensive upscaling/downscaling or create their own GPU.