Right now, it appears that the default setting is easily broken for a minority of use cases and non-intuitive to debug. And that would be good to amend. Better to have it working everywhere and optimisable for power use cases. 

Adding some notes on the wiki probably won't do much to notify existing users - typically copy/pasting from nearby code what I do.

So back to my earlier question - is setting a queue size expensive in the python implementation? If there isn't a technical weakness there, then I'm all for a) warnings and a migration point sometime in the future - it wouldn't be very costly to mechanically search and destroy all rospy.Publisher instances in a ros workspace.