Who else things the guitar products need a up and stroke trigger key to make the playing more realistic
Not sure I completely understand what you're wanting to achieve. Are you proposing adding keyswitches which would allow you to customize the stroking pattern used on the various presets in the library? If so I think it could add a LOT of advanced capabilities, but I also recognize it would likely mean a pretty serious bottom to top retooling of how these libraries work.
Basically the rhythm patterns used are part of the overall sample selected. If I need something very straightforward I can use a stock pattern. If not I can just record and capture specifically what I need within my DAW. To my thinking the articulations one uses when playing an actual guitar are very broad inluding various stroking, muting and picking location and pick holding techniques which I think would be a pretty daunting thing to try and manipulate with computer control actions not to mention the complexity of incorporating it into the sample base. That might be useful and worth it to someone that doesn't play guitar at all, but I'm not sure how many of Native Instruments customers would fall into that category.
Interesting thought though.