Well as it looks now I hopefully have already fixed the "black in" issue. I was able to reproduce it for a second client when I delayed its join to a point when the intro was started within the network body.
The complex thing currently with the intro in Cipher is that the game/mission time is randomized but the intro should render independently from that (light effects ...). So, as the mission.sqm intro sequence can only be used for SP mode, the MP intro must be rendered after the briefing but the briefing should reflect the correct daytime for the mission (which is random). Therefore the time skip, once done for the briefing, is then undone for the intro and redone after the intro - sigh, you see ?
Crazy enough that all this works pretty well under "normal" conditions but as soon as a player connects *while* the intro is running, things start to mess up and thats what still gives me headaches.
I think I just need need a really good mood and plenty of spare time for a relaxing coding session maybe within the next days after that mess i faced the last evenings.
A new option for configuring/disabling the suitcase auto/reveal function is ready for 1.41 anyways, so the chances for an eventually solid MP intro are still there