I have two worries with it.

A capital city like an actual town, makes it so people want to make it nice and build it up. Also the nice part about it, is that for chest shop. People are already there for AH and nation resources. Therefore more likely to buy from as chestshop. I'm afraid that now with chestshop tax, this suggests of yours would decrease the use of them even further.

ah will always be preferred to chest shops anyway, and to be honest with you i dont remember the last time i bought from a chestshop. i have a couple that i use to buy stuff with when im offline but theyre a hassle to manage and empty and generally id prefer ah

I read the suggestion more as this is an optional town type, not a required one, which would solve that problem, also you could make chestshops in the Capital City town type, just needs to be created by a leader or coleader or sell the plot so people can do what they want with it

or ya know they can enable nation perms

Very good idea indeed
Great thinking

trade node is a better name than capital city for this

I like this