I will tell you why bike riders don't have to, and never will have to pay rego.
The RTA says that the primary disbursment of funds from registration goes toward maintaining the road that the cars degrade.
This is why a heavy rigid vehicle will have to pay a higher registration because this individual is doing more damage to the road.
The RTA uses weight as their guide. Which makes sense.
If you look at how the RTA calculates registration and use their own scale, a bike rider (with bike) generally weighs between 150 and 250 times less than a standard sedan.
If you calculate how much a bike riders registration would be based on their weight and how much damage they do to the roads, it turns out that the admninstration cost involved in processing the rego would be more than the actual registration fee itself.
Also, approximately 80% of vehicle owners own a pushbike. If an individual has already paid for how much degradation he will cause in a year with his rego fee, he shouldn't have to pay it again for his bike as he will not be doing any more damage to the road.
In fact, he should get a discount on his car rego because if he is riding 10% of the time and driving 90%, he is doing LESS damage than the standard driver.
So, not only should bike riders not pay a seperate rego, they should get cheaper car rego too
*edit* As for some sort of system to identify riders? I would support that.