I like the concept, but there are issues with it. The size and cost seems impractical for a portable console if there are two controller devices somehow attached to the portable unit. I could understand two controllers (or a spare controller) attached to the dock unit, but two removable controllers attached to the portable unit doesn't strike me as a great idea. In addition to concerns about form factor, how much would this unit cost? What would the battery life be like? Would it be higher priced than the usual Nintendo portable, and if so, how would that affect Nintendo's approach to hardware revisions? Is the TV dock a glorified charging point/HDMI out, or does it host extra storage or processing power? Is the TV dock the supplemental device Nintendo recently patented? How would all of this technology go in one package at an affordable price?
Theoretically this kind of device could allow Nintendo to launch a portable unit that operates with the TV, with a software library that attracts increased Nintendo support, support across the Japanese industry, indie support, family friendly Western titles (Just Dance, Skylanders, Lego) and the odd Western or collaborative exclusive. Think a mixture of 3DS/Wii U catalogues: single versions of the usual franchise releases like Kart, Zelda, Smash, Mario. A mixture of franchises that have been split across systems appearing on one box, so stuff like Kid Icarus, Luigi's Mansion, Pikmin, Fire Emblem, on the same box. More appealingly. two of Nintendo's biggest portable system sellers, Pokemon and Animal Crossing, as marquee releases on this system. Add to that Lego, Skylanders, as I said, potentially Monster Hunter 5, Dragon Quest, the Bravely games, and perhaps things like exclusives from Platinum and Ubisoft, as well as indie support, and you have a really diverse library that could satisfy Nintendo's key constituencies: their high attach rate core fanbase, and the Japanese and family markets they need to hit in order to really make the system viable.
So I think there's a lot of potential in the idea of a mobile powered portable console that has some degree of home operation, but it's still a really risky move. From Nintendo's perspective, I can see why they'd prefer to launch a device that might retain their portable market rather than fight to expand their diminished share of the home console market, but this device also needs to fit in with their iOS/Android presence. Like I said, I think the concept is good, but the execution fraught with difficulties.