I am with you on the 28 being an F2. I feel like a broken record harping on Sigma and Canon to follow Nikon with a 1.8 or F2 lens. That is all we need in the street, I get them wanting the 35 and the 85 that is big and bright and comes with an optional sherpa, but the 28 is a lens that should slip in to a pocket!I'd love a 28 mm fixed lens, though I'd prefer a compact f/2. With IS, doesn't have to be an L. It will always be a street/travel lens for me, on an R body.
And an f/1.4 50 mm with IS!