That's not....entirely true
There are ways around everything you mention. In a strict sense lighting can actually be changed on the fly, I just don't like to do it since it requires accessing the client's console. The only lighting thing you can't mess with is the baked in lightmap. In my unreal server I have a remote control that let's you change lighting at will. As for BSP I helped on a project last year where there was a map that changed on the fly. You should look it up.
There are decent answers for all of this.
Kidding aside I'll chat you in private about methodology. This is something I might do someday and I'll just keep it close for now. End result is yes, there will need to be versioning of the map as people build in it but to an extent it is controllable.
"You damn kids, back in my time we made the items, maps and games ourselves with an unwieldy engine using counter-intuitive crash-prone tools and we liked it so much we built communities around this which nowadays look like cults because they're quasi-parallel societies based on the same old games." -Hellkeeper