-Imran- said:
Does that also increase by 300% from membership?
The Membership perks aren't factorial to the probability rate of a Token Store Shiny at all. Membership will still provide a 1-token discount to purchase itself, however.
As for the publicly unknown rate: as Jinji stated, the rate has never been unveiled, but you'll see statistics of the amount of Token Store Shiny Pokemon obtained per week via
Bluerise's Twitter. Metrically, it won't reveal the underlying rate in any way, but it will at least reveal the overlaying product of the rate—how many were obtained from the current rate out of those that attempted it during that week.