Short walk no worries, I’d be more inclined to buy consumables near the content that I use them in.
Make a separate consumable auction house stall outside every instance that sellers can load their capsules into and just make it list the lower priced ones and operate like a regular vendor.
add a reputation and gear set requirement so you can only load the vending machine while in uniform.
Rewards could be another bag that is slightly worse than one you got randomly earlier but still replaces something in a bank slot and the vending machine worker gloves, no stats but gives the mouse pointer a 12 item slot capacity.
I think these additions would improve raid/dungeon/break room productivity and enjoyment. Questions Comments Queries? Would you like to know more?