I assume that wear will likely result in increased movement over time, so it would be nice if Vans could provide some more specific guidance in the form of an SB or Notification so we know when we need to do something about it.
There are hundreds of different certificated airplane models that don't have a specific specification published for the amount of acceptable play on each portion of their control systems.
It is not reasonable to expect different for any of the RV's.
The burden is on the inspector to have some level of training and experience to make a determination of what is right and what is not.
For E-AB, the assumtion is that the builder knows what everything was like when it was new, so the FAA considers them eligible for a repairmans certificate (I agree with this position)
For E-LSA, an owner could have potentially purchased an airplane that was 95% completed (possible with the E-LSA build requirement rules) so they may not be as familiar with all the details of the airplane. This is part of the reason that for E-LSA you have to take a class to train you on inspecting an airplane.
If you have the training (either being an A&P or Light Sport Repairman Inspector) you are expected to have the enough knowledge to evaluate a mechanical assembly like the RV-12 AST / pitch trim system and find any portions of the system that have more play in them(ball rod end, etc.) than they probably should have.
Based on my experience with the RV-12, I would say that 1/16" play is normal.
1/8" play is an indication of some wear and should probably be looked at during the next inspection.
3/16" is quite excessive and I probably would not fly that airplane until I corrected it.
(it is very possible that the votes for 3/16" were just a guess and it is not nearly as bad as that. The only way to know for sure is to hold the stab. against the nose down stop and then measure the free play with a ruler).