I saw a lot people suggesting something like "Watch Mode", where you can see the spacecraft as normal, but without control.
I think there schould be sub-Modi of this "Watch-Mode", like non-spacecraft-bound, planet-bound and a special for Streamers.
About the last one: A featured streamer could have something like followers, he don't has to add as friends, and then be able set his KSP-MP-Status to "streaming". No matter if he is playing single or multiplayer or on wich server/with friends/wathever his followers could watch him in this "Watch-Mode".