I can't really tell how easy or practicable the chaining of sequences to the more interesting 16 or 32 steps is in practice, be advised that most of the buyers' will do exactly that when working on tracks. The ubiquity of 8 step sequencers may derive from replacing the now inexplicably expensive sequencers that were designed for the monophonic analogue synths people now love and use. But these days it's not Kraut Rock or Ambient Music, but tracky House and Techno people produce with this gear, and if you go for melodies, 8 steps are somewhat repetitive and limiting (yes I know repetition and limits are key to the latter styles, but you get my point, don't you?
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Long story short, I hope chaining procedures for 16+ steps retain their instant accessibility. Like, when working with a 2x8 step sequence, the display or an LED tells which part of the n*8 step sequence we're listening to. While running the sequence, instantly accessing a step and altering it's values should be possible while the sequencer runs through the steps of the sequence, so you can make adjustments while listening to the whole (chained) sequence without interruption.
Probably I won't be using the Knob section at all, having a BCR2000 for this purpose. An optional Firmware without this section, but with an extended Sequencer and Drum section, maybe a total of 8 instruments in the Drum section, or a second voice for the Sequencer … would that be feasible? Maybe with some inexpensive future upgrade via the I2C you mentioned elsewhere?