It's still at an interim state, but I think it's getting to the point where it will be generally useful.
I did a bunch of minor reformatting, and took a several of your responses and translated them into the main thread, removing the back-and-forth: I don't think the discussion is as valuable as a clear statement of the design.
I have a big, sloppy mess of a system involving at least one additional readtable, that breaks under the syntax-control branch. That's going to be my test case for forcing myself to understand this.
Best, r