Not hard to work out mate. It would be a massive deterant allround, if you random test then you will still get an airhead take a chance and have one to many, you do an ALL TEST then everyone will tow the line.
The FIM should send out a memo to ALL the riders in the series stating that they will be tested the day of a GP round at a certain time, including the reserves. If they don't like it, they don't ride. If You want transparancy in our sport thats the only way forward. Quite simple really.
Random test in the domestic leagues as done, unanounced, but the GP's should be an ALL TEST.