> if we modify dis() instead of adding a new function, then
> the default behaviour needs to be non-recursive for 
> backwards compatibility reasons

I don't see how we have any backward compatibility issues.  The dis() function is purely informational like help().  

The problem is it doesn't show important information, list comprehensions are now effectively hidden from everyone who isn't clever and persistent.   

I use dis() as a teaching aid in my Python courses and as a debugging tool when doing consulting.  From my point of view, it is effectively broken in Python 3.