I feel there comes a time when only a sport's inherent dangers exist, and those influenced by outside factors are no longer relevant.
For rallying, I think Group B's demise was probably as close to the end of phase as possible. Senna's death signaled the need for a paradigm shift in F1, and he was the last man F1 lost. Indy Car and Nascar... we'll see. It's all about sponsorers and fans who like speed and a reminder of the serious danger associated with the sport they love (big crashes). Let's hope they make every change they can to implement proper safety tech into their cars + tracks and not kill any more of their guys.
MotoGP, I don't know anything about. But it seems that a sport in which a rider is completely exposed now has the challenge to... basically try and reduce its inherent risks. Because there's only so much they can do to try and make bikes and riders safe.
On a related note, I think this video probably sums up a lot of what I was trying to say up there:
//youtu.be/http://www.youtube.com/watch?v=DZIqdRidlPA&feature=channel_video_title
