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.