None of the shops are restricted or have ever been restricted. You don't need an Omen's Island map to go visit Rathskeller Inn either. The Zombie Den can only be accessed by zombies, alchemy can only be done by zombies, body modifications can only be done by zombies, and nobody else can get your strain so you also have a pretty cool HA base that's limited and not available anymore. In years to come when there gets to be new Zombie Den items you get forever access, we get access during Survival whereas when there were still strains I could keep my skin for 2 months and cure once I got the items I needed.