Even though you normally can find out logically, what prepass is calculated right at the moment, it would help quite a bit to have it displayed what IS calculated in the render-dialog for analytical purposes. It just would make render-optimization a bit more comfortable (especially for people who have not used vray for long).
I would love to see the “1 out of x” prepass being supplemented with some extra info (glossy reflection, pass 1 … ).
V-Ray may calculate many things in one prepass, depending on how many materials plus the irradiance map are using it. If you have glossy materials with interpolation with rate -1, and the irradiance map rate is also -1, then V-Ray will calculate all of these in one pass; so it can’t really provide any more information other than “pass i of N”.