I’m really curious about it.
if you live long enough t’ill that day, you should be able to find it out 
Gold - nope, Gaijin never discounts premium currency.
Berlin cbt bundle - big fat NOPE.
Other bundles - unlikely since the game is still new, but possible.
In-game premium items - possible.
Also, it depends if they are going for a “Victory Day” sale or for a less specific “May Sale”. In War Thunder, Victory Day used to bring discounts to Allied stuff only (no party for Axis), until last year when they turned to a broader May Sale and everything got discounted (through a multiple days rotation).
i bet berlin sale so the ones who bought it get mad and ontop of that the stage 2 will come so i can buy it at a discount and progress right from the beginning.
Dream on…
As a rule of thumb, nothing “younger” than three months is ever on sale.