I, like many other players, prefer not to use fast travel when I play for the sake of immersion. However, I don't mind using it when there is an in-game reason for it, such as the Institute relay. On a different note, I think fusion cores are too common in the Commonwealth to only be used for fueling Power Armor and nothing else. Rather than make them rarer, I'd like them to have another purpose. I propose a mod that allows the player to craft a modification for their Power Armor, preferably the armor torso, that allows the player to teleport to any marked location in the same vein as fast travel, using up a set number of fusion cores with each teleport. I'd probably put this number at around 3, but ideally, it would be configurable. No time would pass, as it is an instantaneous teleport. It would basically act as an Institute relay installed onto your Power Armor.
