Hey - I love(d) to use a fisheye, my (now ex) wife has one that I got for her. It'd be a little awkward to just call her and ask to borrow the lens now, of course, even though we did part on decently good terms (anyone selling a decent copy of the 10-17 in Canon EF mount?) Fisheyes work for some subjects, not so much for the others, and of course it's not something you'd be using every day. I know I would not go to photograph the Three Gorges dams in China, or the Eiffel Tower, without a fisheye in the bag. 
This new Canon lens, of course, is a lot, a lot more specialized still. I admit I have not the slightest clue what I would have done with it in my line of work. I'd joke that Canon would seem to release just about anything before updating the Canon EF 50/1.4, but I guess it's now completely out of question because, duh, it's EF. Now I guess a faster-than-1.8 35mm for RF is the new unicorn, and I guess they'll take their sweet time getting there, releasing RF updates to the 8-15 fisheye, the MP-E, the TS lenses and whatnot before finally releasing it.
This new Canon lens, of course, is a lot, a lot more specialized still. I admit I have not the slightest clue what I would have done with it in my line of work. I'd joke that Canon would seem to release just about anything before updating the Canon EF 50/1.4, but I guess it's now completely out of question because, duh, it's EF. Now I guess a faster-than-1.8 35mm for RF is the new unicorn, and I guess they'll take their sweet time getting there, releasing RF updates to the 8-15 fisheye, the MP-E, the TS lenses and whatnot before finally releasing it.