Canon also patented a 600mm f/5.6 with what appears to be DO optics, but there's no explicit mention of IS, it would be really surprising if a lens like this didn't have IS.
I agree that any 600mm lens that will be produced will have IS. however, the version patented does not have IS.
Only a very few of a large number of patents make it to production.
Here is a translation of the 600mm DO patent application.
http://www4.ipdl.inpit.go.jp/Tokujitu/PAJdetail.ipdl?N0000=60&N0120=01&N2001=2&N3001=2010-145832
