The comments on Plan B have changed my mind (a rare occurrence in the blogosphere).
The problem Subtext faces is that programming languages are boxed in by convention. When you say “Programming Language”, people assume you mean strings of symbols to be compiled into a program. There is a massive background of theory, practice, and technology wrapped up in that conventional meaning. Subtext is outside that box. Some things about Subtext would play well as a modeling language. But when you say “Modeling Language”, people assume you mean “informal whiteboard diagrams”, which is just a different ill-suited box. Some people in the modeling community believe that separating software design from implementation is profitable (for several of the meanings of profitable). I disagree.
Subtext is and will always be about building things that actually work. That makes it a programming language. Adding modeling concepts to Subtext may be a good idea, particularly data-modeling concepts. But I should stay true to the vision of making a better programming language, which is Plan A.
Forgive me for straying from the path of righteousness.