HeroEngine does it, and does it well. But their engine is built specifically for MMO game world development. Because of this they already have a complex replication stack in place that is able to replicate the entire change real time to the other editors / people working in the game world. You could in theory try and do it but as stated you basically need about 4 servers. An area server that plays master roll for the area / level. A repository server responsible for saving all the data from both the clients(people working on the map, and the area itself) the phsyics server, as all clients render physics differently so you need a central control valve to manage the raw data then pass it along to the client’s machines to render. Which also drives lighting to be different as well cause you have to have basically real time light rendering at all times, can’t pre-bake any lighting. Etc so it could be possible but it’s not simple.
Now with that said you can make multiple layers and stack them onto each other. So could have a terrain level, then put a level with buildings inside of it. Steam them together, if I’m not mistaken. So someone could be adjusting the level with terrain, while the other person is adjusting the level with buildings etc. But it takes a bit of a solid team to set that up, from what I have read.