I don't think of a programming language as being the thing upon which I would base my layers of containers. My expectation, as someone coming from not-containers, would be that I should first start with a core-libraries container, _then_ a language container, and then packages on top.
Having this clarity of composition, I think, is important if I need to start bringing other stuff into the environment, particularly stuff that requires compilation, so that I know what to target it against. It also makes it easier to know when a layer needs to be upgraded, for example because of a security issue.
The downside I see is that maintainers of layers higher up in the stack would possibly have to build multiple variants of their layer. But maybe that wouldn't be too big of a problem?