CyberDyneSystems wrote:Are we ignoring physics and optical properties in this wish list here?
Like are these "M" lenses for "Magic"

Most of these fantasy long zooms would be waaaaaay too heavy if they were actually made with modern techniques!

There are allready 500mm f/4.5 primes.. and they weight 7 pounds or more... and cost about $3K
Not likely to replace the lightweight and affordable 100-400mm with a 500mm zoom @ f/4.5. (all the current fairly carriable and affordable 500mm zooms are at f/6.3 at the long end)
F/4.5 & 6.3 don't bode well with Canon teleconverters. I know that the 200-400 f/4 would be big and heavy (just like Nikon's) but it would also be compatible with both the 1.4X and 2X (on 1-series bodies) and retain autofocus. Something intriguing about a clean 800 mm lens.
I'd like to break the 400 mm f/5.6 barrier (and I know that some day, I'm going to have to bite the bullet and snag a 500/4).
A zoom @ f/4.5would be even heavier than the prime,.. and 500mm @ f/2.8

Or 560mm @ f/2.8 ??
Yeah, 500/2.8 would be huge. 560/5.6 would share the diameter of the 400/4. In fact, the 400/4 DO with the 1.4X TC is 560/5/6, so I guess that lens is already available.
Absolutley collosal! We're approaching 1200mm f/5.6 size here!!!! This is a $90,000.00 lens we are talking about and one that no current standard tripod is rated to hold.
That's a lot of telescope! 
200-400mm f/4 is doable.. in fact I just handeled Nikons version of this lens a few weeks back.. again.. no way is this a 100-400mm replacement.. it is larger than the 300mm f/2.8.. nearly as large as the 500mm f/4 prime.. and about the same weight. (very nice lens though!) With a 1.4X it is a 280-560 f/5.6 zoom... not bad at all.
Yes, that focal length is high on my list. I know it isn't as portable as the 100-400 (which really is pretty compact for its focal length), but it is a logical progression from the 70-200 lens.
What I would like to see?
400mm f/5.6L IS with focus speed of the current 400mm and modern IS
AND/OR
Update the 100-400mm (you can knock 100mm off of the wide end and make it 200-400)
Keep it f/5.6 at the long end so it's just as light as the current one,. BUT update the AF so it is closer to the 400mm primes speed,. and replace the IS with the 3rd gen standard.
Make a decent 100-300mm for gods sake,.
Emulate Sigmas 100-300mm f/4 EX but add IS

How about a 70-300 f/4 IS. 
Naw, Canon won't make that, since it would compete with the DO lens.
Canon needs to make a competitor for Sigma's 120-300mm f/2.8 as well. This will of course have IS,. it will cost over $3K and weigh a little more than the prime,. but it will rock for sports.
Yes, that would be a very useful focal length at that aperture. I would expect it to be more expensive than the 300/2.8 prime though.