Thanks for the patch.  Adding the feature is somehow easier than I expected.  After moving the sample text to module level, which I considered doing before, saving edits for the duration of an IDLE session turned out to also be easy.  

With 11 point Lucida Console, there is room for 5 more lines, without erasing anything, before anything scrolls off the top.

I expect that saving changes across IDLE sessions would be much harder and likely not worth the effort.  I think that exploring font choices is likely rare enough that there is little need to do so.