Some of the ADR discussions seem to revolve around trying to create a formalized 'use anywhere' ADR model which does looks suspiciously like UML. The general concept (a historical record of the development of the architecture) sounds good, but a one-size-fits-all approach sounds like a bad idea. ADR approachs should probably be heavily customized to fit each project/codebase.

Some people might say, "but if we had standardized ADRs we could efficiently compare different codebases" but that's going back to UML.