I've tried compiling it for the PI. The problem is that the code is a total mess. You need to compile 87 projects back to back to make it happen, and all of those need to be edited for work on the PI. I've even tried to pay a programmer friend of mine to clean the mess up, he took one long look at it, laughed, and said nope.
You should all do like I do. Write bug/suggestions reports knowing they'll be mostly ignored, and then deal with whatever the hell gets released and work around the limitations. In a way, it's his software, he supports it however he wants so we have nothing to complain about really. But to me, Klystack feels like watching the world's fastest race dog chained to a post and malnourished. Wasted potential and no love.
As for FM. I personally see no need for it because there's already tons of softwares out there that do it very well. What's lacking most for me is a couple of options in the synth engine like noise pitch independant from the instrument's pitch, fine tuning, some more shapes in the wave editor single-cycle generator and reorganizing the screens into something that doesn't feel like every new option is tacked on 'where there's place for it'. And a 'live' screen where you can mute/unmute and loop/unloop on the fly, and in sync with the tempo.