A few thoughts about the tycoon section of the game.
Could there be a possibility to sell/buy engines or other components from other companies, or even large sections of a vehicle? Either building the engine/car yourself, or just buying them wholesale from the other company. Of course you need to have somewhat decent relations with the company (that is, not big rivals in the same region or vehicle type). For example, the Mitsubishi Eclipse in the early to mid 1990s was also sold as the Eagle Talon, and the Plymouth Laser, with only minor modifications between the vehicles. This may have been suggested before, but it leads to my next point.
That the tycoon mode should have relatively average middle of the road engines for the AI companies, with some semi-rare exceptions. I don’t want to tweak for 2 hours on an engine, for the AI to have an engine that either completely breaks the rules, is better because the computer is far better and faster at optimizing an engine then me, or because a forum user made it, or so on. Such an experience for me would be… depressing. Of course, not that such a thing can’t happen, it just shouldn’t happen all the time, especially not early in the game.
I’ve already suggested the first one, the answer is ‘maybe’.
The second idea I totally agree with but a difficulty system would help.
We are planning on integrating an engine market, yes. Ideally we would like the player to have the option to be completely focused on engine building, too, specializing and selling superior engines to other companies. Of course that would not be “the best” strategy in regards to turnover and potential profits, but interesting nonetheless.
AI generated engines really would be pretty simple in their generation, no cheating allowed for the AI either. A good engine tuner should always have the edge over the competition, and there probably won’t be highly specialized engines to buy either, and if they are, for a hefty price. 
You could also do a body market. Basically this means that you can get a body (former platform) and buy it. Then when building your car, you can get this platform setup etc and are restricted to using that aprticular body for the car. This way you trade some freedom of picking whatever you want for cost efficiency. You still get to pick your own fixtures, though.
A different approach could be buying the complete body with fixtures and all, and you get to edit or replace up to 1, 3 or 5 fixtures on that body to style it like you want, again with the same benefits of cost efficiency.
Maybe just a rough idea, but I hope it comes across. This way you can have both a body and engine market in the game with some benefits to it.
What about buying und selling productionlicenses, not only for multiplayer, perhabs via steam Workshop. If someone buys some licenses from you you get some ingamemoney in a match were you building that car if ingametimeframe matches.
