The conclusion of issue 26993 is that we should apply this issue to 3.6.  My target for inclusion is alpha2, scheduled for June 12.

I am aware that this will require changing file names in existing patches on the tracker.  But they nearly all have the much larger problem of needing the new tests that I will now start to require.

Nick suggested above that breaking code should be more palatable if introduced in a context of overall improvement, including better clarity in supported APIs.  Here is a start on the IDLE What's New entry that should be part of this issue.

"Idlelib is being revamped to make IDLE look better and work better and to make it easier to maintain and improve IDLE.

Part of looking better is the use of ttk widgets.  As a result, IDLE no longer runs with tcl/tk 8.4.  It now requires tcl/tk 8.5 or 8.6.  We recommend running the latest release of either.

'Revamping' includes renaming, refactoring, and consolidation of idlelib modules. As a result, imports of idlelib files that worked in 3.5 will usually not work in 3.6.  At least a module name change will be needed, sometimes more.  Information will be added to idlelib.  In compensation, the eventual result with be that some idlelib classes will be easier to use, with better APIs and docstrings explaining them."