Branching is a powerful tool of VCSs like git and mercurial. I'm not gonna expose all of the useful things you can do with branches, I'm sure you know this already.
I understand why you want the VCS to be easy to use (for artists for instance), and therefore without branches. But I think you could have two modes of work:
- A simple mode, without branches, for the artists
- An expert mode, with branches, for the devs
The devs could then create branches to create new stuff / refactor / etc. while the artists work on the main branch (e.g. develop).