Official Need for Speed teaser announces 'Full Reboot', coming fall 2015.

Well, there it is. After skipping a year (2014), this is the first sign of life for a new NFS title, which, surprisingly, is simply called "Need for Speed", nothing else.
Just a teaser at 34 seconds (the full trailer is announced for June 15, shortly before E3 2015), you could say it has a distinct Underground-like flavour, and the official description seems to confirm this:

The new NFS game will feature deep customisation, authentic urban car culture, a nocturnal open world, and an immersive narrative that pulls you through the game.

Needforspeed.com has been updated as well, and interviews with studio Ghost Games' executive producer Marcus Nilsson have appeared at Gamespot and Eurogamer. Need for Speed (2015) is set to appear only on PC, Xbox One and PS4, but not on PS3 or X360 anymore.