First of, some of the artists are using gluon, although most are using the classic UI because it gives a more detailed view (which is handy IF you understand it).
Secondly the single branch workflow is working out very well for us indeed.
Pushing our branch to a new repository and pulling it in again every time we need to update it will indeed work in our use case since we don't want to merge later on.
Though I find it hard to believe that this isn't a fairly common use case. Even building for different platforms might need changes in settings, shaders and sometimes even logic. For big differences like those, it makes sense to make a new repository and pull in any changes you need. For smaller things though, it might give quite some overload? Making a new repository for each small temporary task might be a bit too much.
While further thinking about this and about the locking system, it makes less and less sense to me why the acquisition of a lock would be global but still the effects of a lock are separated from branch to branch. I'll illustrate with another example:
Firstly note that we do not in any situation want to stop using locks, they are key to making sure no work gets lost.
Suppose we are two weeks before a major deadline but due to some unexpected issues, we still have a whole new feature to implement. Problem: we haven't decided in which of two ways we will make it work. We thus split our dev team of 6 programmers in 2 teams of 3. Each of them will be implementing one of the two ways into the project. Also suppose their changes cannot be merged because, for example, everything is done in blueprints.
The two teams start working on two different branches and keep using the checkout system to make sure they are not editing the same file within their team (and because they are used to using the UE4 plastic plugin to checkout things). But by doing so, they unwillingly block the other team from editing those files at the same time, thus stalling their progress.
I think their are many other use cases where the lock acquisition should not be global and I can't think of any cases where having it global would be useful (although there probably are some but I'm just biased).
Although I can definitely see the use of the distributed locking system, as would make proper feature branching possible. I just don't see why those globally acquired locks are the default behavior currently.