Kaz's remark about appealing to the overwhelmimg majority of players being casual seems to indicate a continuation of a low difficulty level in career.
I don't see why they can't just have differing degrees of difficulty in career mode. Vary the payouts, restrictions on cars and tires, length of races etc. and you can easily go from super easy to super hard with the check of a box. The game is way way beyond the point where it has to be one size fits all. And the good part is, these options don't have to take up a lot of programming time. No cars to design, no sounds to record, just adding a few more layers and options in menus.
I don't think the difficulty is the problem. It's easy to make it difficult... right now PD's difficulty is scaled by how much of a handicap the driver starts out with. You can never get pole position, always start from 5th and further back, sometimes 12th, etc. More difficult currently = more handicap. What we want is actually a specific kind of difficulty that is instead based on an intelligent and genuinely fast-racing AI.