Well, I used WinMerge to have a look at the changes. Most of the changes were internal (CPU, Memory, Flash, EEProm, etc.)
There weren't much GUI changes or new functions. Only the Game Overridables got a new option, as far as I can remeber.
If you got some questions, just ask and I'll have a closer look at it
I made a quick measurement between the old and the new core, and I got 10% slower performance, but that wasn't a very accurate measurement.
And as long as pokemonhacker improved compatibility, I will deal with it.