There could be another option added to the banner in its settings tab that would allow players, that are not whitelisted by the banner, to open doors and use crafting tables and things like that but not be able to destroy any blocks in the banner protected zone. There could also be another option to set which would let you decide if the players can open chests or not. The last setting that could be toggled would be an additional option to decide if it lets anyone in or if it lets players from specific factions with required minimum alignment to use the banner's special pass. This idea would be useful with my other idea about npcs that could be hired to live in a player's city because it would allow players to come to the city and trade and use the different buildings without the possibility of grieving. Hope this is a useful idea!