Just an editor mode (3D or otherwise) that allows you to dit your mission live with other people connected to your client. Simply go into the MP browser and start a server. there will be an option to start an 'editor gamemode' along with password settings and max players. Anyone who joins is able to participate in a live session of editor.
Multiplayer editor will have both pros and cons. But for the sake of the suggestion I will focus on the positives for now (not because I'm an optimistic fuck).
- Active learning and knowledge sharing of the complex array of mission-making techniques the system has to offer,
- Ability to provide troubleshooting assistance to a friend who is having issues getting a trigger to perform as desired, or any other problem they may face,
- Productivity. Many hands make light work. A mission may take days or even weeks to perfect before it's even playable, more than one person working on it at the same time will effectively divide the time taken for by y (being the number of people).
- Collaborated ideas to reduce the chance of "editor's block" (a medical condition similar to writer's block when a mission maker runs low on ideas and becomes frustrated, and contemplates suicide).
To wrap this up I would like to stress that this is only a suggestion and I don't expect it to even become a feature. I just like to get my ideas on paper where I can look at them later, but seriously, consider implementing this because it seemed like a good idea at the time.