There is a good answer, it's called a pop up message...man that's basic UX stuff that many browser tools
already figured out...
The problems you are listing are really but really easy to solve, a team working on a project are in constant communication, there can even be an implemented chat and all, stuff like "not being able to work" will never happens, there are also soooo many softwares that have collaboration features in real time even softwares for video editing.
I will suggest you Ashley to do some research firts instead of saying no from the start, since it's not something impossible to do and that many softwares do already, all the problems you are listing are really but reaaaaally easy to solve for an UX expert.
The problem goes deeper than simply adding a popup button, it's easy to add a popup sure, but is that's necessarily not good UX, especially in an application with so much inheritance. There is no one size fit all solution and it's not "reaaaaally easy" to solve if you want to keep a good UI and UX relationship. However this still doesn't make it an impossible task, it just requires research and testing and a lot of implementation.
In the end It would essentially become version control, and then as Ashley said:
[quote:2bsy3fnr]I think the permissions idea where you can say lock a layout and only do level design is much more feasible. But then why not just use existing source control mechanisms? Is all this really better than that?
At that point, the time would be better spend on integrating a existing service like github or gitlab than making a new service from scratch.