I decided one thing I needed both for Sebastian and PyLing was a graphical shell, sort of like the interactive shell in IDLE but with the ability to display inline graphics as part of the real-eval-print loop.
Mathematica is a good example of what I have in mind, as shown in the screen shots at http://www.wolfram.com/products/mathematica/tour/page2.html
wxPython's PyShell looks like it would be a great thing to work from but as far as I can tell, the underyling wxStyledTextCtrl doesn't support inline graphics.
Looks like Qt's QTextEdit doesn't support inline graphics either. So Tkinter is the only one whose rich text widget supports this!
It turns out to be really easy to do what I want in IDLE (although for some reason this doesn't work in IDLEfork - still investigating). Just added one line to ModifiedInterpreter in PyShell.py to put tkconsole in the locals dictionary.