Speaking for myself, the physics aren't much of a concern for me because FM4's were already the best on consoles, and they give me faith in FM5's being even better. So long as sticky grass is dealt with in another way (either made an option, or replaced with a different system to deter cutters, or even better, both), and aerodynamic effects don't kick in at 100mph on the dot, I'm really not too concerned.
The severe lack of genuinely new metal to the series is my main qualm. Of course, it's a double-edged sword; the less new metal, the more FM4 cars can return, and there was a whole mass of good ones.