I respect original ideas that would add to the racing and improve the quality of the driving experience, not arcade-style ideas that have already been posted and re-posted this forum about a dozen times already in the past five years.
Having real companies like HKS, BBS, Koni etc would cost the devs money to begin with because those companies would want license fees - that same reason keeps real-life cars (except the two BMWs, the MRT and the Raceabout) & tracks out of LFS. Also, I doubt many LFS players would want to spend their real money to make their virtual cars faster. If they did, the racers with the most money would of course end up with the best parts, putting the racers with less spare money at a gross disadvantage. For some people in the world, an S2 license just by itself is a major purchase. Start adding to the costs by forcing people to spend money to be competitive and watch people go and play something else very quickly. The thing people like about LFS is that you buy your license and then you compete on a level playing field, with driving skill being what decides a race result, not the money you've spent on parts.
This "tuning" debate has been brought up on this forum so many times, a quick search and five minutes of reading would have given you a great view of the arguments for and against it. If people seem a bit short-tempered it's because everybody who suggests tuning thinks they're the first to think of it, while a forum search for "tuning" (or even "tunning") would have revealed the opposite.