I've used Plantuml extensively, and still use it a bit, now and then. I don't remember ever needing or even wanting bi-directional editing. There's a lot of interesting things in terms of syntax and semantics here, but I really do not see WHY they are tackling a very hard problem on top of an already not easy one.
As a counterpoint, I also use PlantUML a lot mostly with C4 and I thought the bidirectional interaction looked very cool. I think one benefit might be getting those who don't think in specific syntax and code involved in progress elaboration of the diagrams by using the GUI portion.
