Cool idea about implementing stop branch markers. I also had something similar implemented, but in form of comment-like boxes. But eventually I ditched it in favor of coding the thing directly. I failed to come up with good unified solution to handle cases where branches are interlinked somewhere in between. Maybe you will have a better luck at this. Great job in any case.
Just wanted to add that I ended up using texture arrays for core layers of landscape shader and reserved flow control for triplannar layers. Frame to frame render time consistency ended up being a major factor.