What do you think of "Time served" grades for 2nd Dan or 3rd Dan for people who "don't have the time" to prepare for their test! although double time served is required ie for 2nd Dan you'd have to wait 4 years and 3rd dan would be 6 years. I personally only feel that medical conditions should be the only reason for this.
Dan grades are already essentially time-served grades. The problem with performance testing at the black belt level is that at a certain point being a black belt isn't about performance, but about wisdom and experience.