To answer your question cudwieser, I am a little less than halfway through chapter 5, and as soon as I heard the details about the coming update, I deliberately held off on finishing the game.
I really felt that the choices of Runner cars that can go up to 399 was sorely lacking. I was using the BMW M5 as my 'final' Runner car, but now that we are getting the Alfa Romeo, there's no question I will use it instead.
My final lineup will probably be this:
Drag class: Lamborghini Diablo
Reason: Lamborghini is my favorite car brand and the Diablo was the last true stick-shift lambo - It's too old to beat out newer supercars in grip racing, so the drag class felt like the perfect spot to put such a car.
Drift class: Nissan Fairlady (derelict)
Reason: I've always liked the old Fairladies, but before actually trying it out, I never though I'd like it enough to want to finish the game with it. It drifts so effortlessly though, I really love driving it.
Race class: Lamborghini Huracan
Reason: Again, Lamborghinis are my faves. I would've preferred to finish with an Aventador, but during the heist mission where you steal one, I was vastly disappointed with the handling. After watching Youtube reviews, I see it's not just me. Apparently the Huracan is the best Lambo in the game, and that's good enough for me. (I haven't actually unlocked it yet, so I can't speak from experience).
Off-road class: Aston Martin DB5
Reason: I was disappointed with the selection of off-road vehicles that would go to 399. When the DLC dropped for the DB5, I knew I had to use it as an off-roader, just because it's so rebellious. I love the look of the superbuild - it's absolutely mental.
Runner class: Alfa Romeo Giulia
Reason: I've been in love with the Giulia since it was first unveiled. I think it's the most beautiful 4-door sedan currently in production. Can't wait to flog it around the cops as Jess.
Speedcross: Mini Countryman
Reason: It's hard to classify Speedcross as a thing since it really doesn't play much of a role in the story, but what the heck... I like the looks of the Countryman and it feels good on the Speedcross tracks. I could be talked into the Ford Focus RS though...
Of course I own many more cars, but those are the ones I've chosen to go through the final part of the story with, for no more reason than personal preference.