I have no particular opinion on FM. The only thing that worries me is like you say: if klystrack starts doing too much, it'll start being less oldschool/chippy and more of a DAW-ish thing. But before new implements, there are bugs that could probably be fixed quick:
-pressing 'loop from current' when your cursor is over a channel with no pattern in will loop the 64th row of the previous pattern instead and is insanely annoying
-arp effects carry from song to song. if I have a 037 on channel 1 in song A and then load song B, the channel still has the 037 applied. If you play a 0F0x instrument in channel 1, it'll arpegiate.
-sometimes the sequencer view at the top of classic view seems to kind of desync with where you really are in the song. If you CTRL-K over a pattern to make a copy.. sometimes it doesn't work. What really happens is that a pattern was indeed copied, to the next available pattern as expected, but that the pattern copied is another one, and it doesn't show up on the sequencer window. If you press enter a couple times to switch the cursor between sequencer and pattern editors, you'll see that upon coming back to the sequencer your cursor is pointing a few patterns before the one you thought you were on before. It's that pattern that's been copied. I don't know the specific trigger for it however. But it happens often enough that has a precaution I always quadruple-enter before I CTRL-K a pattern (which I do all the time)
Also.. instead of converting some FX busses to 'masters', you should just let every instrument export to all FX busses. You just toggle which busses it sends to... like [ ]1 [ ] 2 [ ] 3 [ ] 4 etc. That way people can make their own, and as many master channels as they want, and it also opens the door for some creative FX work.
And a simple live mode. Load two songs side by side, each with a volume fader. That's it
¯\(º_o)/¯
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