Yesterday, Nintendo has a successful unveiling of the Switch, formerly known as the Nintendo NX. Following the brief teaser, there are many questions that remain about system specifics. The Switch games are on GameCards, so some hoped that 3DS backward-compatibility might be available.
There are a number of things that stand in the way of backwards-compatibility on the Switch. The Switch is a single-screen system, requiring some sort of work around to transfer over many Wii U and most 3DS games. This is something that Nintendo has dealt with before though, with DS support on the Wii U allowing for single-screen options.
In the case of the both legacy systems, the Switch has a different, Nvidia-powered chipset, meaning there would need to be some software emulation solution. It's possible that Nintendo has already figured out software emulation, meaning these games might be purchasable over the 3DS eShop, but that is unlikely to help folks who already own the physical versions.
Nintendo also confirmed that both Joy-Con controllers would come packed in with the system, but didn't mention the Nintendo Switch Dock. This opens the door for the Dock being a separate purchase.