I believe you Chris, for three rows - it's push that's the problem. But what about having four rows? You can't keep a constant relationship for the 2 acc rows, on push, because you'd need 8 extra buttons, per group of three on the 2 diatonic rows, but the 'slippage' by one button on each octave should be acceptable, because that's what you get on pull anyway (and it's a 4-button repeat on my acc row, for both push and pull).
It would seem to me unwise, naive even, to extend a melodeon layout to four rows, though I imagine it has been done(?) The thing would weigh a ton and would mitigate against one of the great pleasures of the box which is dropping onto 1 row technique, when that's right (some might cry "always)
I learned "off row" playing in France. Basically I drop to pull only and have a number of practiced tracks. I play it as a CBA. So "pull only" doesn't matter much. All the blues stuff I like seems to work on that way, though some eg Bb blues/ myxolydian need that b7=Ab. It is on same button as Bb, so gets a little flick. Works, but some runs of notes don't play through.
I'm cool on that, it becomes "your sound" and we could say the same of 1 row play. Constraints can be good? Yes, with a 4th row you could circumnavigate all that, at the expense of learning more scales, but go to such effort when you could do it all on CBA with … essentially six fingerings to cover diatonic, harmonic and melodic minor, blues scale and the 2 symmetric scales? Virtually all the other scales in use are modes of those.