HDS would be a strange name, but I'd expect announcement in 2 and a half years, at e3 2016, with release either late 2016 or early 2017. Unless they pull another GBA and kill off the 3DS sooner than later. O_o
Hardware-wise, I think they may be able to use Wii U as a baseline considering how it already uses so little wattage. Put in 2GB RAM, a pair of 1280x720 screens, 3.5 - 4.0 inch screens. It will look pretty nice with a small screen at that resolution. It'll probably have some graphical effects newer than Wii U / PS4 / XB1 due to technological advances these next two years will probably have, similar to how 3DS although less "powerful" than Wii, it has a more modern GPU with neat graphical effects that look very nice. Obviously it won't reach polygon counts at Wii U's level, but it'll be close, and a good little handheld.
