Technically, the board may be able to support it. It doesn't mean Apple are willing to put it in. The logic board of current generation MBPs takes up about a third of the chassis, with the remaining space being made available to the battery packs. The board is stuffed with chips and caps. You could extend the size of the board, but that would cut into battery space. By which you'd have to program something clever to use less energy during low priority tasks. Or you can bring up the chassis size. Ideally, Apple could do something like a mezzanine board but that would take up space and you'd have to make sure the RAM on that board is handled as well as the mainboard/logic RAM.
