I'll throw my hat in on the feedback... looks great!
https://github.com/openscad/openscad/pull/4478#issuecomment-...
My pet use case is: "My naive approach as a programmer would be: `pen := new Pen(q,r,s,t); box := new Box( pen.L, pen.W, pen.H )`" along with being able to sometimes work with the whole pen, and sometimes touch the pen vs. the cap separately.
Since it's all javascript, it seems like there's a chance that this use case would work (ie: `p = Pen(...).render().getWidth()`)? Additionally, your intermediate step screenshots really makes it seem like a SketchUp-ish GUI would be perfect! Obviously a ton of work, but SketchUp's "grab face + extrude / push", but if it were "sticky" to the underlying parametric components seems like it'd be an awesome combo... something like group/components, but backed by code instead of GUI-only (or GUI-centric) editing.
The interactive region extrude feature is designed specifically for fast modeling at the expense of making the model "not so parametric". When user pick a region, the raycasted point is inserted/hardcoded in the code. e.g extrude(100).pick([100, 100]) So if the sketch dimensions change, there is a chance the point will fall outside the region boundaries which will break it. It is preferred to use proper boolean operations in sketch mode to define regions while keeping it parametric.
The interactive region extrude is there for when you want fast modeling/prototyping.