Let me say right up front that I think it's great that Canon is already trying to push the boundaries of what's capable with the RF lens mount. The fact that anything as crazy as a full frame 28-70 f2 exists at all is great, and I hope Canon keeps pushing.
But honestly, from the standpoint of "would I actually buy this," I'm having trouble getting excited about this lens. It's massively big and heavy, and massively expensive. And for all of that, what do you really get? It's not quite as fast as a prime (not even close to the fastest L primes), and it doesn't have quite the wide angle capabilities of a 24-70. I feel like it's a lens that's painted itself into a corner by trying to be everything all at once. And as a result it doesn't really give you the speed you'd expect from a prime, or the focal length range you'd expect from a zoom.
Maybe it's just the way I shoot, but I never really expect one lens to do everything for me. If I want speed and a nice shallow DOF, I'll use a prime. If I want the versatility of a zoom, I'll use that. A 24-70 2.8 is, to me, limited enough in its zoom range without losing another 4mm in the wide end. So honestly, while technically I'm sure it will be a great lens, it doesn't really seem to excel at having a large zoom range or a very fast aperture, which makes me wonder if it would ever be worth dropping $3000 on.
But honestly, from the standpoint of "would I actually buy this," I'm having trouble getting excited about this lens. It's massively big and heavy, and massively expensive. And for all of that, what do you really get? It's not quite as fast as a prime (not even close to the fastest L primes), and it doesn't have quite the wide angle capabilities of a 24-70. I feel like it's a lens that's painted itself into a corner by trying to be everything all at once. And as a result it doesn't really give you the speed you'd expect from a prime, or the focal length range you'd expect from a zoom.
Maybe it's just the way I shoot, but I never really expect one lens to do everything for me. If I want speed and a nice shallow DOF, I'll use a prime. If I want the versatility of a zoom, I'll use that. A 24-70 2.8 is, to me, limited enough in its zoom range without losing another 4mm in the wide end. So honestly, while technically I'm sure it will be a great lens, it doesn't really seem to excel at having a large zoom range or a very fast aperture, which makes me wonder if it would ever be worth dropping $3000 on.