When are they coming?
I have confirmed that the new EF 200-400 f/4L IS 1.4x will indeed hit some retailers before the end of May, and for the others the first week of June. Canon Canada expects and is telling retailers that they will have limited stock on May 27, 2013 in their warehouse. Retailers will have theirs a few days later.
There will not be a lot of lenses available on the initial run, most reps are saying only “preordered” quantities will be available until at least the middle of July.
If you have your preorder in, it looks like you should expect your new lens quite soon.
Canon EF 200-400 f/4L IS 1.4x $11,799
If you don’t mind being gouged, you can also get one from a 100% ebayer that will ship it to you on May 31, 2013 from Japan.