I followed this thread with much interest from an "end-users"
perspective - To me such a feature seems to allow for many
interesting things which go beyond just plugging static
images between the text (eg. in PyCrust). It seems
that then anything (even applications ?) could be embedded.
Anyway this is said without any idea on the technical details 
and just to express that I also would be happy about
something like the mathematica worksheets
(I am mainly thinking of scipy where this would be really cool,
in particular as there wxPython is already used in chaco for plotting).
Arnd