You already have "shuffle" racing in the "quick race" mode. The same guy that raced shuffle races in GT5, races the quick races in GT6. Most have no clue on tuning. Which is why one would go to the shuffle rooms. And most think they are driving a bumper car seeing that most quick races end with wrecks and the dreaded "penalty". You can get the penalty even if you are the driver being hit.
NO, Sorta but no, no and NO.
Shuffle is nothing like "Quick Race" mode. In a shuffle room you could run different PP levels, tracks, weather, anything but pick the cars and tires.
I do race in quick race mode occasionally for the easy .cr and most of the time I let them all crash then drive around them.
Many shuffle racers could tune just fine and raced in PP rooms as well. Some simply hated GTs broken tuning system and didn't want to waste time in it. Others like me, found that the best drivers raced in shuffle or spec rooms A.K.A. stock/no-tuning, same make and model.
Also a good shuffle room ran races very frequently. So an hour of gameplay had a lot of races in it. More than you could get in a PP or even a spec room.
Considering most PP rooms marked "clean", back in GT5 online days, had terrible drivers in them. I found if I wanted a good clean races the best place was a "clean" shuffle room or spec. Being fast in a shuffle room required skill with any vehicle type. Not just a wrecking ball driving style found in many PP rooms.
I figure the main reason quick race mode is so dirty is because you can't kick bad drivers and no rules about clean driving are set.