Wow! a new 400/4 with ISII and improved optics surely.
Light in weight so tough competition for the heavier 500/4 and the possibility of a good 560/5.6 - probably much better than the 300/2.8 with 2xTc.
I doubt if it will be much better than a 300 and 2xTC, but it certainly won't be noticeably better, it at all, than the 300 and 1.4 TC (to make 420mm and f4). Now if you like the horrible bokeh the DO can create and don't want a lens as flexible or as high quality as the 300 then have at it.
I cannot see a reason for this other than Canon's refusal to give up on DO, meanwhile there is a good market out there for other premium headline catching lenses, the MkII 100-400 will be a cash cow whatever price it comes in at and a 400 f5.6 with IS would clean the wallets of those scared off by a new 100-400 price point. The 45 and 90 TS-E's are desperately overdue, the 2.8 ultrawide zoom has been a sore point in the Canon lineup since, oh, ever, but they clearly can now make good ultrawides so what's the excuse for this delay? The MkII 800 is a headlining niche lens that is sorely wanted by those that need it, to have your longest lens outperformed by your second longest and a TC is an embarrassment. The 85 f1.2 could do with a spruce up, the 50 f1.4 is crying out for the "slow it down and put IS in it" treatment, it just goes on and on........
Canon's lens strategy gives me more concern than their sensor strategy.
it takes years to design and develop a lens. I think the last time any of the big two commented on how long was nikon - and they said it takes 7 years from start to finish.
DO is such a tactical advantage to canon - and we don't know if they correct bokeh related issues, and most that have used the later models of the 400DO have found it no wanting.
It depends on what lens, it would take a design team about three hours to design a 50mm f1.8 IS, and considering they have the glass, they have the parts, they have everything, they could probably have a working model just after lunch.
Now the DO dead end has taken 13 years to come up with an update for a lens that will still appeal to about 20 people, which do you think would make Canon more money, selling a handful of 400 f4 DO's that still perform like crap and depreciate like a Syrian bankers domestic property portfolio, or a mass appeal 50 that costs next to nothing to make and can be slotted into the $499 slot?
Canon have stuck with DO because they want to, they want to make that square peg fit in out round lenses, and they will spend countless man hours on keeping it going for no other reason than they want to and they patented the heck out of it so they can. Sure in ten years (weren't we saying that thirteen years ago when the 400 came out) when DPP can "adjust" for the aberrations in post it might work, but seriously, who cares? When DO is ready for prime time then bring it to market, I am all for it, in the mean time keep the people who pay the bills happy (us customers) with lenses we want, we need, and we can afford.
+1 the last thing anyone wanted to hear / read on CR were the words "diffractive" and "optics" this close to frikkin photokina!