Hello,
A product have just one single warehouse.
But a product can have several categories.
So it is not possible to assign a warehouse to a category because it would break the rule that a product have just one single warehouse (and it would not be possible to know which one to select).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.