I am polishing off 3.5.0 (It should be out in a week or so. Still quite a bit to do, but not much time :).
Anyways, One big change is the SashWindows.
Instead of one on each side, there are now as many
as you want (well, up to 100, though I doubt anyone would go that high) on each side (Top, Bottom, Left, Right).
The code for handling adding and accessing these panels has changed quite a bit, and any plugins that use panels will likely need to be updated to continue to work. This is a heads up, the code is still too warm to put out on the forum cool.
I realize this is a bit of a pain, but there won't be too much stuff to change, the code will look much cleaner (and be smaller), and you will be able to do much more with the interface of drpython.