Great to see Pharo on HN. I picked Pharo and Glamor [1] for a new IDE that I'm working on [2] and it's a real pleasure to work with so far. I didn't find anything else in the same league.
[1] http://gtoolkit.org [2] https://github.com/studio/studio
[1] http://gtoolkit.org [2] https://github.com/studio/studio
So when I say that I picked Glamor I mean that my plan is to extend the Spotter and the Inspector to be able to navigate and visualize the internal data structures inside my application.
Does that answer your question?
See also this thesis on moldable tools: http://scg.unibe.ch/archive/phd/chis-phd.pdf