Welcome back, Mike...
I agree with a lot of what you say (trying to keep Nigel happy, these days!) but one thing I'm not convinced about - I've been using a 128 note arranger for years now. I can't honestly say I have EVER heard notes dropping out. Not in the busiest passages of SMF's, not in the densest of styles, not with quite big layers being played as well.
Now, that's not to say that MAYBE it hasn't happened. But I've got a pretty picky ear (as most here know!) and if I can't ever recall hearing it, well, that's good enough for me!
Personally, I think there are so many, many much more important things to worry about and wait anxiously for them to be improved than polyphony... speed of response, for one. I can layer up all 5 polyphonic Keyboard Parts on my G70, put stereo sounds on to all of them, and play fast repeated chords, and not hear the slightest of flams..! Pretty damn good, IMO. My Kurzweil can't do that, my Triton can't do that, my old G1000 certainly couldn't do that! I'd rather have 128 voices of instant response that 256 that you can't use all of them without it bogging down...
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An arranger is just a tool. What matters is what you build with it..!