Need for Speed games used to be developed like clockwork. From 2002 to 2013, there was at least one Need for Speed game a year, sometimes more. So there wasn't a great deal of time for alternative visions.
But around 2003 and 2004, there was two different views on where the franchise could go: Need for Speed: Most Wanted, and Need for Speed: Repo Man.
A history of the game's pre-production phase is outlined in the first several minutes of the latest Raycevick video, which you can view below. It touches on the game's pre-production phase, and some of the clues left behind in the NFS games.
While Underground 2 was being developed in early 2004, a team at Black Box started working on what Most Wanted would look like. It's not sure when Mia Townsend's role shifted — she was originally shown as an underground racer, third on the Black List — or whether Black Box originally intended for the player to be the underground cop all along.
Most Wanted would eventually adopt a grungier tone, rather than the over-the-top styling seen in some of the pre-production art. Raycevick's video is also a good reminder of how much tuning difficulty settings needed in oldschool arcade games: the grind of working through events until you could get a modified, or better car, could be brutal.
I'd still like an Underground 3, that said. Surely someone at EA could make this happen - hell, I'd even take it as a mobile game.