I think we are seeing phones replace handhelds for most situations. I think of the 3DS as a kid's portable (no offense intended for adults that play it - yall enjoy your games) but I think that's the target market.
And with everyone carrying a powerful phone, I just don't see a big market for a something like the Vita in the US. With the PS4 launch, I think they will be over-saturate the market and confuse customers if they release the Vita TV. But as other said, there is too many alternatives.