Hardware scalers were never designed to run 2880x1800, 3360x2100 and 3840x2160 resolutions. The max has always been 2560x1600 for quite a long time. And it's not as if using 2880x1800 uses just a bit more power than 2560x1600. If you can't do it in hardware, then you have to use software, and performance pays a big penalty.
Wouldn't it be more prudent than to wait until hardware scalers could run those higher resolutions, as opposed to using software, so there would no or very minimal performance penalties?