I think I understand what you mean, but I'd say this unbounded "richness" is precisely what you must avoid in a programming language. In a programming language you want constraints, not freedom. Your visual language must convey specific, unambiguous information and not be open to interpretation or confusion. A program is inherently closer to a formula than to art.
As a complete and irrelevant aside: I wouldn't assume visual artists will consider category theory diagrams artistically uninteresting. Artists are an unpredictable bunch, capable of finding beauty in the most unlikely things ;)
Name-dropping category theory via including a diagram in artistic work doesn't mean that the diagram itself is visually relevant. It would essentially be functioning as a sign rather than an image. (Feynman diagrams are a totally different story.)
As far as richness goes: I don't think programming languages have to be austere. "Richness" might be a divisive term to use for it. I just mean high degree of expressiveness. Also, I guess, a high degree of elaboration. A rich type system is not necessarily a dangerously self-indulgent, inconsistent, dangerous one—it might instead be the end result of a rigorous process of elaboration according to strict criteria.