With the current DDR3 SO-DIMM technology, we will not see a macbook with more than two memory banks. They just take up too much space and increase power consumptoin, and don't offer much in terms of performance.
At least for compact notebooks (Air, Ultrabooks), the trend seems to go towards soldering the memory right onto the logic board... this might provide other options to increase the bandwidth, but I don't think this is really a bottleneck for laptops.