Very little chance it has backwards compatibility.
I kinda want one. I dont necessarily get truly portable with my handheld devices, but I do like to play them in bed or on the couch while others are watching something on TV. This would be a cool way to do that.
And as things will essentially combine the efforts of Nintendo's console and mobile teams, it should mean a whole lot more content. And should also be more attractive for 3rd party developers who essentially get to create a console and a handheld version of their game without any extra work.
Dont want to pay more than $300, though. At Day 1, I'd buy it. Otherwise I'll wait til it drops in price.