Sorry, I wasn't as clear as I meant to be in my last message, I was suddenly rushed and didn't realize I'd left out what I meant to say, which was:
Now that Andrew has committed Todd's fix to issue 5066, idle.rst and help.txt are very well-aligned. I believe the transition could be made now with no negative impact on the quality or usefulness of help.txt.
Here now is a patch to Doc/Makefile and Doc/make.bat to add an 'idledoc' target. I haven't been able to test the Makefile change yet, but as it's a direct quote of your suggestion (with correction), Georg, I figure it ought to work :). I have tested the make.bat change, though, and it works well for me.