LDT, about that "no keys, no sound" issue, I meant you are forced to hold down a key, so you don’t have your hands free for other things, like improvising some part on a keyboard. I still find that’s "not preferable" if that’s the only mode it should work, but I also said that a Hold feature is needed. So in essence you have both ways.
I’m not trying to be negative here and all ideas are welcome, but for me the main principle is it should work as musically and logically as possible.
In the past I had several experiences with a program called Artwonk. I’ve made stepsequencers with all kinds of bells and whistles possible. One of the things that was high on the list: How can I make a sequence pattern less rigid so that it follows my chordinput in "some way"? I do have some ideas and they come from experimenting, not just some wild thoughts.
I don’t have an Octopus, but I do believe that the Octopus is flexible enough to go a step further without eleminating excisting features. If some sort of chordrecognition is possible, then you have the best of both worlds. The power of a stepsequencer and still be "musically free" because you can change scales on the fly.