Updating a GUI everytime someone wants a shop would be a pain to create. Everytime a new player wants a warp, it would mean that we would need to create the warp, change the GUI, update the plugin for that GUI, and reload the plugin. Same happens when someone goes inactive or the player doesnt develop a shop at all.
As you said, suggestions are good but you need to think before doing them, this one requires permanent update of a plugin everytime someone wants a warp, which will clearly not happen. Staff are here to have fun too, not to be tortured with unecessary things.
Regarding the option of having a specific place for the shops, as I said, we want to promote player interactions, so we want to promote towns (or claims in Horizon) to build markets.