Why is this thread still going? You probably spend more time here than any delay caused by afking. I doubt that lazy afk grinding is really a big problem, at least I havent seen it on my server and even if it happened it's easy to avoid that player (e.g. pick a different track).
If you really want to see people go less afk, get SE to put less race deciding items into the first chess. If I'm out of stamina at the beginning of the race, it doesn't matter what I do. You really want me to sit there, pretending there is a point in continuing just so you can finish the race 5 seconds faster? Punishing DNF racer won't change anything about that.