Going to happen.
But if the prior IS non-Ls are any indication, Canon will give up maximum aperture to get IS. This may end up being an F/1.8 IS or F/2 IS. The idea being 3-4 stops of IS is worth losing one stop of speed, and I'd presume that IS with an ultra large aperture design would be large and heavy, something the non-Ls are not known for.
- AHS