For whatever it's worth, we've done similar stuff with node.js, operating from an actual OS-generated (i.e., not reinvented) core dump.[1] The difference in approach here is that we don't require the app to load anything, and we don't change its behavior -- we perform all of the inference from the dump itself, using extensive knowledge of V8.[2] It's great to see other dynamic languages discover the merits of postmortem debugging; for us, it's been essential for developing node.js-based services.

[1] http://www.joyent.com/blog/mdb-and-node-js

[2] http://www.slideshare.net/bcantrill/goto2012