every of those squares locations would have to be specified to be allowed to be a zone where shop on offline mode is allowed, and would be hard for players to know where is where and what is what, best solution would really just make the free offline shop everywhere in all towns and just let users pick where they want to set their shop, who likes how it is stays where it is, others can move shops to towns.
from my point of view, it would decrease a bit the lags for the users with lag trouble in GH(i personally dont), and it would help the towns gaining some more "life".