So, I've been thinking about RAM in the context of the other components in the Wii U, and I'm thinking that Samsung's 20nm DDR3 chips might be what Nintendo's going with. They've been manufacturing them in 4Gb densities since late last year, and it's made on a much smaller process than any other manufacturer uses, which means much lower energy consumption and heat. Samsung advertise that 4GB in a laptop consumes just 0.97W at 800MHz (1600MT/s), and the RAM is rated up to 1067MHz (2133MT/s), although obviously with higher power usage. This means, given a 128 bit bus, Nintendo could run it at 800MHz to give 25.6GB/s bandwidth in under half a watt, with potential to go as far as 34.1GB/s at 1067MHz at no more than a couple of watts. Seems perfect for Nintendo's need of low power without sacrificing performance.
However, I can't find out if they're available with 32-bit interfaces or only 16-bit, which would be necessary if they want a 128-bit interface with only 4 chips.
As a side note, here's a thought on clock speeds. Assuming a 120MHz DSP:
CPU: 1.92GHz
GPU: 480MHz
RAM: 960MHz
It'd be possible with the aforementioned RAM, it would fit Nintendo's apparent desire for clocks which are clean multiples, and (assuming 640 SPUs) it would just exceed the 600GFlops which people seem to be focussing on.
Edit:
Just being pedantic, but they also do a line of CISC chips called the z/Architecture for mainframes.