doctest was intended to deal with the standard CPython terminal shell.  I'd like to keep it that way, but recognize that everyone wants to change everything into "a framework" ;-)

How many other shells are there?  As Sergey linked to, IPython already dealt with its shell conventions, and PS1/PS2 differences account for a relatively tiny amount of the 600+ lines of IPython-customization code they'd need anyway.  That is, I don't see that this would be of much value to IPython.

So people who "need" this already figured out how to do this - and there aren't many of them anyway.  I'd leave it alone.