> The biggest problem with these tools is scalability and maintainability.

This has been my biggest complaint with both Unreal and NI Reactor... you can build some brilliant things, but not without creating a mess of connections that becomes very difficult to reason about, let alone work on. A lot of production "visual programming" diagrams are spaghetti code, without comments or a changelog you can study.

While written code tends to the same way (just try diagramming the class tree in most software), at least we have tools for dealing with and reasoning about it in text form.