Possible, but I don't see your reason for wanting them as it massively adds to cost (the glass they have to put in) and it just gets heavier and heavier, even though they're sharp as heck now and 2.8 is really good for zooming. I was surprised to find my 24-70 II A LOT heavier than my 70-200 f/4 IS.
As you know, it'd be a better option to go for a prime to get apertures larger than f/2.8 due to the lighter construction

But then again, I'd probably be VERY tempted into buying a 70-200 f/1.8L IS