I checked the measurements on new oversized malt pipe, and it looks like it would physically fit in older generations (at least the 3.1.1 I had onhand to measure), BUT it would sit REALLY low and require some type of work around for the second bottom screen. I think you could physically get it to work, but I suspect the lack of space between the bottom of the malt pipe and heating elements would mess up the heat distribution and liquid recirculation, causing any number of unwanted problems.
I would love to be pleasantly surprised and be able to use the new malt pipe to get bigger grain bills into my 3.1.1, but looking unlikely.