In my view these flowchart systems look like they work well for simple cases, but for more complex cases you end up with a pile of spaghetti and endless scrolling which makes it hard to even find anything. I doubt it would be easy to track dialogue in this type of system if you had a novel-sized amount of content (e.g. 300+ pages, 80,000 words). You'd have a huge scroll distance and everything scattered over an enormous area with incredibly long lines joining tiny fragments of text.
For that I would break up into smaller units of "flow charts". Or even implementing a kind of "collapse/expand" system. Group one particular set of location, and then collapse/expand it to make it clearer in view.
It would be harder for the developer for the game maker engine to write, but would be easier for the end users to use. :)
But I know you, Ashley, are very set against this idea and that I can respect, that's YOUR software.
As for the going to JSON route of things.
I know how to import JSON (in a very general idea as I have used it, however together with RexRainbow's plugins, to import levels made in Tiled, in a wildly different type of game)
but I am just not seeing how I can organize the dialog branching in a visual/easy way when coming to a book size volume, with spagetti branching, in a such linear format as JSON. idk. Even more so when I need to expand the game (expansions is planned to gradually release new releases - demo - first release 1 release 2, 3, 4, 5, introducing more and more characters, ending with 100+ characters and interactions between those.. )
I just can't wrap my mind around how to organise it. It is my major issue.