Nintendo has already stated they're not going to compete with Sony for graphics. I've expected for awhile that the NX to be basically be Nintendo's version of the TG16 and Turbo Express Portable. Both handheld and console will be sold separately, but the games on each system will be universal. I think the NX will be no more powerful than Wii U, and may or may not have Wii U backwards compatibility. Imo it's going to be more like "you didn't support us purchasing the Wii U? Go fuck yourself." The reason I don't think it's going to be more powerful than the Wii U, is because the handheld will need to be as powerful as the console and both systems will use cards. The concept of the Wii U is basically a DS. The HDTV is basically the same as the top screen, the touch pad is the same as the bottom screen. So the NX might use the same concept and the portable version will be a DS style system. Or they might do away with the DS and use a regular controller, going back to a Gameboy style system.

As was already stated, the benefit of both systems playing the same games is that development costs are reduced as you'd be developing it for a single unified system. Not only would this benefit first party developers as they wouldn't have to split resources between systems, it might interest other third party developers, maybe more niche studios, to develop for this system instead of the another console, because they'll be able to capture the interest of both the handheld and console market by developing a single version. Nintendo hasn't had much third party support in comparison ever since Sony came to the market. The portables have had a lot of great software that was exclusive, but not so much with their consoles. I think this hybrid console is really going to be a necessity if Nintendo wants to continue to do both portable and console and still be a competitor in the market. I also think it's Nintendo's last chance to show gamers they're relevant on consoles and that if the NX fails as a console, Nintendo may go exclusive to portable development.

I think if it's a hybrid console it'll succeed though, because this benefits gamers. Gamers can purchase a single copy of the game at retail and play the game portable or on home console. So people can purchase the console if they're more interested in playing on console, or purchase the portable if they're more interested on portables, and then you'll have the people who purchase both, playing the console while they're at home and the portable while at a friends, work, etc.