New 100-400mm and 7D seems to be quite the couple these days. For sports and wildlife peeps, its piece of standard kit. Here's my predictions:
1) internal design like the 70-300
2) same f4.5-5.6 aperture
3) weathersealed like the modern L lenses
4) modernized IS
5) price bump but not as much as we think...
6) updated focus
7) Bokeh-licious nine bladed aperture (parity with other L lenses)
Thing is, canon can dip into their cooperate parts bin for bits (weather sealing, IS update) to modernize the lens to keep parity with the L line without radically changing the price point or market for this lens. I think thats critical for them. For wild life and sports, weathersealing is paramount, modernizing the IS and focus, some modern glass to boost contrast, its in line with the updates to the markii's we've seen in the 24-70, 70-200, etc.
An F4 version would be so heavy and pricey, and with the 200-400mm on the horizon, it could potentially cannibalize that market. With the new ISO performance of the newer bodies, and in camera lens corrections, the Achilles heal of CA & vignetting can be minimized. So that last 10% of perfection for many lenses can be corrected in software, keeping the price down.
for the 7D, I'd say a 2 stop high iso performance boost so that 6400 becomes the new 1600, courtesy of canon's brainy Digic chips, hopefully retain the legacy of AF speed & flexibility along with 10fps, in keeping with the 1D-lite legacy.