I was curious re the filter size. Firstly, I have no idea re lens design, I loved the article on this site about it but beyond reading that I have no clue so this is just ramblings
The filter side normally relates roughly to the front element size but a increase in filter size could just be to reduce vignetting from the filters rather than specifically a larger front element. I picked two lenses and compared the filter size between manufactures. All 35mm full frame lenses.50mm f1/1.4
Leica 50mm f/1.4 SUMMILUX-M 46mm
Sigma 50mm f/1.4 EX DG HSM 77mm
Canon EF 50mm f/1.4 USM 58mm
Zeiss 50mm f/1.4 Planar T 58mm
Nikon 50mm f/1.4D AF 52mm
Sony 50mm f/1.4 55mm100mm 2.8 macro lenses
Canon EF 100mm f/2.8 USM 58mm
Sony 100mm f/2.8 55mm
Tokina AT-X 100mm f/2.8 PRO D 55mm
Canon EF 100mm f/2.8L IS 67mm
There is quite a bit of difference between lenses! The same differences occur with 300 2.8 lenses although it is tougher to get all the info as they are usually drop in filters. However, after looking at patents it is often the case that lenses are not actually the exact ratings advertised. Sometimes a f2.8 is a 2.9 or a 3.0, sometimes a 50mm is a 47 mm etc. Just as happens with motorcycle engines some rounding / wishful thinking / marketing occurs. Until canon release the lens (fingers crossed!) we won't know for sure. They could have increased the front element size just as sigma did with their 50mm, they could just be moving the filter thread further out to reduce the impact of using filters. Canon increased the front element size and filter size on their L versions of the 100 2.8 macro and the 70-300 over the non L versions. Both lenses improved image quality. Again, I do not design lenses
but it seems like a modest increase does help! It is also not a huge increase, we arent talking 105mm screw in filters here so the costs arent insane. It would be a pita to have to carry an additional set of cpl and different rings for the nd grad system.
I just wish they would hurry up and release it!