Instanced areas are coded a certain way to restrict/confine certain actions and events. Destiny's netcode could not handle a shift in weapons hot/cold in the tower. For it to run smoothly you would have to enter the instanced area like you would selecting the tower/crucible and would be redundant since you would have to go to orbit/patrol anyways to test the weapon. A work around would be to have similar coding to a "Darkness Zone" in the Tower where when you enter the area it allows you to equip a weapon and try it out. But again this has to be another instance and allow for First person mode. like i said, the netcode could not handle it.