In a nutshell, it doesn't work. Using Fred Brook's venerable terminology, the essential complexity of programming is too difficult for nonprogrammers. Even if you entirely get rid of the accidental complexity... and visual layout does not do that, it's full of incidental complexity involved in the layout itself... you still can't get non-programmers into a programming situation, and trying to get them into a concurrent programming situation is just sheer insanity.
And we know it doesn't work because it has been tried. Over and over. Ad naseum, as in, yeah, I'm sick of hearing these ideas as The Answer as if nobody has ever heard of these before. Tell me what's different about your solution and all the other people who have tried this.
Edit: it's too bad that the programming model is getting lumped in here with the visual programming schtick. Those are two different things. (Of course the former would get no PR without the latter.)
I suppose "dataflow" is an overloaded term, and the fact that its various meanings have quite a bit in common doesn't help.
Slide 11 of this talk makes the same point, but with less words: http://www.scott-a-s.com/files/debs2013_tutorial_slides.pdf
I believe FBP primarily deals with data flow, not control flow, but the "flow" in FBP seems to be left intentionally ambiguous.
What I discovered after a while, was that there was a tiny sweet spot where it was nice to do complicated things without writing code, but that it had huge drawbacks. Queries became ridiculous, for one.
And very soon, the stuff I'd build using the Views module was 'complicated' enough conceptually that a normal SQL query would not only be much faster, but easier and quicker to write. The fact that this query could be version-controlled and didn't live in a database was nice too...
Move fast and break things. Replace what breaks with stronger pieces until it doesn't.
Reminds me of the recent "One weird trick!" article [0] and lines like, "the simple solution dietitians don't want you to know!"
Content aside, that kind of thing immediately sets off alarms for me.
[0] http://www.slate.com/articles/business/moneybox/2013/07/how_...