I did not hear that the M3-m is going to be 19" rack-able, though..... I was under the impression it is going to be the top piece that is attached to the keyboard as a standalone.... Sort of like the old Oberheim Xpander in form factor.

That's a shame, IMO. I prefer the protection of rack gear.
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An arranger is just a tool. What matters is what you build with it..!