Most of the additions are in the engine switch.
By using Unity, I was able to target higher resolutions (I currently test at 2560x1440) and still hit 60fps. Then of course I added some post processing. At this point, I'm just trying to get it equivalent with the PS2 version. The infrastructure is there to add more cards. I could open it up to modders.
I'm not relying on any exotic libraries at all, a Linux port would just be a matter of me setting up a Linux install and testing it.