I think the standard 2nd row will fold flat. Now, maybe they'll first deliver some thousand cars with the non-folding 2nd row, while they do the finishing touches on the folding 2nd row, but the deliveries of the standard 2nd row should start before xmas. Once they announce that the standard 2nd row will fold flat, I doubt it will be easy for Tesla to find very many thousands of general production reservation holders willing to order the non-folding 2nd row. So with the ramp up, they will run out of firm orders pretty quick.
Tesla could try to get more people into a Model X with non-folding 2nd row by being quiet about the folding 2nd row for as long as possible, but the result will be mass cancellations and anger from buyers who receive the non-folding 2nd row days and weeks before the launch of the folding 2nd row. This leads me to conclude that the best option is to simply announce folding 2nd row in October, with deliveries before xmas.