Late reply I know but:
What kind of objective validation would you suggest?
The validation one seeks depends on ones training objectives imho. First one must have clear objectives and understand the critical skill sets required to achieve those objectives, then work on developing them. The final aspect is the evaluation or qualification method.
If the goal is effective physical waza (effective meaning that a technique should have the desired effect even if the attacker is uncooperative), then one can use testing in the form of sparring with varying levels of resistance and unpredictability. When ones techniques start failing regularly or the attacker's attacks start landing regularly it is time to stop and evaluate what is happening, where the breakdown is occurring and look for a method to fix or improve the area that's lacking. When the failings are addressed, keep increasing intensity and expanding the scope of attacks and aggression until your response fails again. Then repeat the analysis of the problem to find a new solution within the Aikido paradigm.
A similar approach can be used for different aspects of training depending on the goal of the practitioner.
Just my 2 cents.