My bullshit detector is screeching here. The easy one is that 768MB of RAM isn't a power of 2, and hence would require an odd number of memory controllers: that'd mean with 192-bit or 384-bit, and 6 or 12 DRAM chips, as this is the standard kept for consoles, video cards, and mobile devices. Both interface widths are beyond reasonable for a gaming console: the Xbox, Xbox 360, and PS3 all used 128-bit interfaces with 4 DRAM modules: other consoles were all smaller.
The easy money is that people, trying to get the scoop, are just fabricating numbers and claiming "inside sources" they cannot cite; IGN did this for the Wii, after all. These sort of claims don't hold up to any reasonable scrutiny; the 3DS, after all, already nearly rivals the 360, so why would a home console be only marginally better?
The 360 has shown that it actually is difficult to do 720p with HDR+AA on 7th-gen consoles: some games (such as Skyrim) are as low as 576p, which only measures in at 0.59 megapixels. (the PS3 just can't even do HDR+AA, period) Hence, simply taking the SAME games up to 1080p would require a whopping three and a half times the power of the Xbox 360. Even just going from 720p to 1080p requires an improvement of +125%. Merely being 50% more potent simply wouldn't cut it, especially given that developers have already announced 1080p ports of 360 and PS3 games for the Wii U. So this pegs the power at a MINIMUM of 2.25x. And Moore's law suggests something well beyond that.
I'm outright discarding the figures given out-of-hand: adding to the suspicion is that nothing's claimed other than the makers, and the QUANTITY of RAM, but not the type: if they'd even talked to an ENTHUSIAST, let alone an actual developer, they'd be able to get real, important figures like that. Instead, the easy money says that this is 100% fabricated. A more logical guess pegs the RAM at 2 GB (and that assumes that, in spite of the 3DS, Nintendo is still stingy on RAM quantity) with the RAM being either GDDR5 or XDR2. (Nintendo skimps on quantity, but always buys the fastest RAM) The power would be closer to around 4-6 times that of the Xbox 360 or PS3; in other words, 4-5 years' advancement through Moore's law.