Making multiple owners to a mincraft world

Minecraft we really need tjus idea and it is that there are multiple owners to a world like my freind made this world but when he is 9fl8ne i could still join that world and i know we have servers for that but we also have tons of wotlds that people have hardcore and ut is not a server and some people dont have access to servers loke me so if you could make an update where people can join other wordls by a 'KEY' that the owner has given to you then you can join and play the ssrver when that owner is offline thank you for your time