Depending on price, I don't see the Switch doing well in the West beyond selling to the people who are already Nintendo buyers. It's cool as a high powered handheld, but the console element is probably the weak part of its design. All of its appeal lies in its portability, and it's not even that portable considering its size. We don't know any specs, but it's probably going to be about on par with the Wii U, if not slightly stronger, due to the portable nature.
Saying that I commend them for trying to appeal more to the hardcore market with stuff like Skyrim and offering portable versions of traditional, non-Nintendo games, with full controller support. Personally, I'm not sure the console will be for me, because I actually despise Nintendo games beyond Smash Bros, but depending on what games get announced I will be paying attention just in case they have something that does appeal.
Personal estimate on life time sales: 45 million units. Significantly more than Wii U, due to less novel appeal and potential stronger focus on third parties, but less than 3DS due to tablet competition, lack of portability options, and leaving room for any unforeseen inevitable fuck ups that Nintendo are prone to.
