Will the 3090 kingpin include the watch dogs legion promo code?

The promotion ends October 29th, likely before the Kingpin release.

With every operation of this type, there's always a " While supplies last " type of thing. That allows the products to look more enticing and for the game editor to choose how many keys they want to give without having to divulge anything or make retailers edit their pages to remove the operation from the product, that would make them less enticing. 

Especially if a retailers is selling an inflated +250€ card (in France anyway) you can bet your booty that they'll never take it off until the operation expires in order to look the inflated price feel less like a robbery. 
 
That being said when the Kingpin will come, the operation might already been ended anyway.

mcarger
i still don't understand when and how  i'm supposed to get my watchdogs legion bundle key, i bought an rtx 3080 xc3 ultra

The process to obtain the key comes from where you bought it.  If you bought it from direct from EVGA, then you can go here to redeem it: 
https://www.evga.com/arti...get-watch-dogs-legion/