If the population continues to increase without development of more efficient transportation there is no reason why there wont be an increase in motorcyclists in the city. The traffic will slow down and peeps will naturally opt for alternative transport - just like our east asian brothers. The question is over the next 100 years will there be another alternative means of transport that will be more efficient than motorcycles - i.e. flying cars, airbourne motorways, high speed tube systems, teleports
???
An increase in motorcyclists will likely see an increase in safety for riders - maybe dedicated lanes, speed limitations, technically improved bikes etc.