There's many demands for the game, naturally. Does it need a story? I have no clue. Would it work without one? NFS:HP2 back on PS2 did it...but could it work today? Again I got no clue, it depends how talented the team is behind the making of the game...
All I ask, having played extensively NFS2015...please, get a solid handling model. No bugs, no fuss. A good handling model that's predictable but realistic enough to be labeled NEED FOR SPEED. NFS2015 was crap solely because of the handling, it had all the customisation in the world, but that couldn't save it from being a HORRIBLE experience to drive.
So, please devs of new NFS game...learn from your mistakes, then impress us!