IS is so much better than f/2.8 for landscape stuff, f/2.8 isn't much DOF. f/4.5-5.6 and IS does soooo much more.
When I started shooting macro, I had to realize how many things in the natural world actually move a tiny bit, I never realized until I tried longer exposure times. Often the same applies to landscape, IS doesn't freeze leaves from jiggling or water from waving. In this case, neither shallow dof *or* IS will help, what's really required is a high iso high dr camera which Canon doesn't have yet.
But the IS will certainly have some benefits for a handheld video, or lowlight photography when you don't have/ can't use a tripod. Of course it can't help freeze subject movement, but equally, f2.8 isn't the best aperture for a typical landscape shot anyway, so it's always going to be a compromise. I'd rather have the IS available than not- of course, how implementing it affects pricing is another matter!