SWC was introduced with the EF24mm f/1.4L II USM in the 2008 announcement. A year after 200 & 800.
200 & 800 do not have IS mode 3 & Power Focus amongst other things. New paint job is also missing. It also lacks a Kengsington lock.
200 has 5-stops of IS
The current 400/2.8 is 16% lighter than the 800 and does not have the separate optical front element that serves as protector. It is now integrated onto the super hard front element. This is one component that can be removed in the 200 & 800 to lessen weight.
1/3rd or 1/2 stop is a difference between stopping the action and having slight blurring. ISO can only do so much even on the flagship 1-Series. Shutter speed dictates whether the subject is frozen or has subject motion blur. ISO determines exposure amongst other things.
Canon lenses with less fractional stops.http://www.canon.com/camera-museum/camera/lens/ef/data/wide/ef_28_18_usm.htmlhttp://www.canon.com/camera-museum/camera/lens/ef/data/standard/ef_50_f1.2l_usm.htmlhttp://www.canon.com/camera-museum/camera/lens/ef/data/standard/ef_50_18.htmlhttp://www.canon.com/camera-museum/camera/lens/ef/data/standard/ef_50_18ii.htmlhttp://www.canon.com/camera-museum/camera/lens/ef/data/standard/2006_ef_85_f1.2lII_usm.htmlhttp://www.canon.com/camera-museum/camera/lens/ef/data/standard/ef_85_18_usm.htmlhttp://www.canon.com/camera-museum/camera/lens/ef/data/telephoto/ef_200_18l_usm.htmlhttp://www.canon.com/camera-museum/camera/lens/ef/data/super_telephoto/ef_500_45l_usm.htmlhttp://www.canon.com/camera-museum/camera/lens/ef/data/macro/ef_50_25.htmlhttp://www.canon.com/camera-museum/camera/lens/ef/data/macro/ef_180_35l_usm.htmlhttp://www.canon.com/camera-museum/camera/lens/ef/data/ts-e/ts_e24_35l.htmlhttp://www.canon.com/camera-museum/camera/lens/ef/data/ts-e/ts_e24_f35lii.html
“Size matters not. Look at me. Judge me by my size, do you? Hmm? Hmm." - Yoda
Advances in materials science will allow for lighter 800 at a faster f-number than what was possible today.
It'll be out in 2020, more than enough times for the optical boffins to figure things out.
$35,000 would be cheap, by 2020.
I can see a 4.4, 4.5, 4.8, 5.0 or 5.2 f-number in the future.
By 2020 I may not be doing photography anymore as serious as today but still...
Canon also uses nanocoatings, like Nikon's Nano Crystal Coat. It is called SWC by Canon, Subwavelength Coating. All of Canon's new lenses use SWC on multiple elements. Nikon has no advantage there. Flare control on newer Canon lenses is second to none, and one of the biggest reasons I love Canon glass.
Canon's EF 800 f/5.6 L IS was the first lens to use Canon's 4-stop IS system. That is the same 4-stop IS system that is used in the new Mark II generation of Canon teles and superteles. It is also the same 4-stop IS system used in the EF 200mm f/2 L IS. The IS system of both the 800/5.6 and 200/2 is most certainly not out of date. It is actually the current state of the art, and the system that paved the way for the Mark II 300, 400, 500, and 600 lenses.
Weight is probably only area where there can really be significant gains, although the current 800mm lens already made a fair bit of headway on that front by being almost two pounds lighter than the old 600mm f/4 L lens. Canon might be able to improve IQ as well. The 600mm f/4 L II is slightly better than the 800mm with a 1.4x TC, so there is probably something Canon can do to put the 800mm back on top. Is it worth it, though? The margin is very slim...and as a prime supertelephoto, the current 800mm is still a phenomenal lens. I've never used the 200/2, but from what I've seen, it too is a phenomenal lens capable of producing some unbelievably good images with the most mind-blowing boke you've ever seen.
When it comes to aperture, if the difference is f/1.8 vs. f/2, it is trivial, and doesn't really matter. With the insanely good high ISO performance of Canon cameras these days, a third of a stop bump in ISO is trivial.
As for the 800mm, Canon doesn't usually use intermediate f-stops for maximum aperture on their prime lenses. It would either be f/5.6 or f/4. An f/4 800mm lens would require a 200mm entrance pupil. That is GARGANTUAN! The single largest entrance pupil in Canon's entire lens lineup is the 600mm f/4, with a 150mm entrance pupil. An 800mm f/4 would require a 33% increase in front element size. The diameter of the 600mm II is 168mm, so the front element is probably exactly 150mm in size. Can you imagine a lens with a 200mm front element?!? The barrel diameter would probably be 220mm! Not only would such a lens be HUGE, it would be heavy, even with Fluorite elements...much heavier than the current 800mm f/5.6 L (which is actually still fairly light...lighter than the previous EF 600mm f/4 L by a fair margin, again thanks to Fluorite elements, as the current 800 is still a modern design).
It would certainly be an amazing lens, an EF 800mm f/4 L IS. But it would be a significant feat of engineering to make it practical for anything outside of relatively permanent, stationary use on one hell of a beasty tripod. That is nothing to say of the cost. The EF 600mm f/4 L IS II costs $13,000. The current EF 800mm f/5.6 L IS costs $13,500, and it has a smaller entrance pupil than the 600mm. I can only figure an EF 800mm f/4 L IS would cost...$25,000...maybe $35,000?
I don't see either of these lenses getting an increase in maximum aperture. Its either not logical, or not practical.