Peripheral vision in LFS is easily as good as it is IRL. The view you get in LFS is far better than what you see in an actual GT car with high sided seats, with the click of a button you can turn your head and are only limited by the high sided seats, not so easy IRL tightly strapped in with a HANs device and helmet weighing your head down. In LFS we don't have steamed up dirty windows or race in less than perfectly clear conditions. Not to mention the magical mirror which has nothing obstructing it, or the fact that there's no disadvantage sitting high enough to get a good view. Just trying to move one of these cars around a parking lot is a nightmare in reality because you can't see a thing, let alone trying to race them.
We already get too many clues as to where other cars are, the mirror, seating position, ease of looking round, and much more distinguished sounds of other cars which you don't hear well enough to place in reality. There is no need to add extra artificial aids to LFS. If you can't place other cars in LFS without using the 90 degree look buttons then your doing something wrong and definitely shouldn't try racing a real GT car.
Equally if you blast the horn all the time and consider there to be an issue with people not seeing you have you considered they have seen you and have decided not to give room to the stupid over aggressive wanker blasting his horn at them?