To me, this is mostly a solved problem for casual contributors using the web interface of GitHub (and I assume gitlab, Bitbucket, and others). If more "serious" contributions need to be made, learning the basics of how git works isn't that difficult - branching, commits, and merging are basically all that a novice user needs to understand, and they're pretty easy to explain concepts (even if it means you're telling White lies about how it works under the hood).

We don't expect the average person to understand the tools and workflow of a mechanical engineer working with SolidWorks PDM - we shouldn't expect the average person to understand git (which is basically the software equivalent). I've never disagreed with the arguments that git is confusing or difficult to learn for non-software-developets, but I've never really understood why that's a problem.