I agree with your general comments, as I hate writing glue code and my interest is primarily for DSP and simulation applications, for which I already admire it.
I'm still not sure I understand your proposal. How do short IDE-type addons solve the problem of integrating siloed codebases with each other? The way I see it, the only way forward is
1. Convince a language person that first-class support for algebraic metaprogramming is important
2. Convince someone from each of the fields {numerical methods, linear programming, finite element methods, graph theory, etc} to export an interface to the language in #1, possibly re-structuring their entire codebase to do so
3. Documentation, convenience schleps
I say "convince" because the problem of making a Mathematica replacement is far enough down my todo list that I have no choice but to be realistic about the fact that I probably won't be that person.
On a tangential note, this latest demo looks very very close to the sort of thing Bret Victor has been talking about over the last year or two (http://worrydream.com). If you haven't checked it out I think it might be interesting to you.
We build networks of lots of different kinds against our own codebases and databases. And personally I've done a bunch of experiments around visualizing code in the past.
Unfortunately, I don't think I, or anyone else at the company, has convincingly cracked the problem yet. Generally, the visualizations look pretty, but they aren't "tactile" or practical enough to be useful.
But you've convinced me that it would be worth digging up some of my old experiments and writing a blog post around them, so that at least any progress I've made can be carried further by other people.
I would certainly be interested in seeing that. I have a lot of that sort of work looming in my immediate future.