Why Kontakt only?

The script adds an internal tuning table to the instrument. Then it modifies the way the instrument responds to midi messages so that the new velocity keyswitches can adjust the pitches of individual notes in the table.

It is impossible to do anything like this with a midi plugin or an audio processing plugin chained before or after the instrument. You need the capability to modify the way the instrument itself responds to midi.

This script relies on this unusual feature of Kontakt; you can modify the notes with a script AFTER the midi notes are received in the instrument. In this way, Kontakt lets you hack the inner workings of the instrument itself.

It would I think be permissible for someone to write another sample player able to play Kontakt scripts using the published Kontakt script manuals as a basis, through the same laws of interoperability that permit Wine to emulate Windows. But would be a big task, many programmer years probably. Not heard of anyone who has done that.

You can't write a VST plug in to do any of this, because there is no midi message in the standard protocol to change the tuning of an individual note.

So, any VSTi would need to be reprogrammed individually to support this feature.

Similarly other sample players, software or hardware synths would need to have their code modified to use this feature.

They wouldn't need to use this script. The programmers would surely program their software directly to respond to thesse midi messages in the same way. It might be quite simple coding depending on the architecture, but because of the need to tune one note in the channel one way and another note another way, it is totally outside the scope of what can be achieved by a normal plug in.