I wonder whether Canon will introduce new R lenses with rear drop-in filters? Obviously, not every lens makes sense... Why bother with a filter drawer on something with a 72mm front filter size and no vignetting restrictions? But they've given themselves the room to do it on a 17mm tilt/shift, or a 11 mm lens (whether prime or zoom), or even something with a merely inconveniently large front element (200-500mm f5.6 or the like). Fast supertelephotos with impossibly large front elements usually have filter drawers in every system. Could they have put a drawer on the 28-70mm f2? Its 95mm filter size qualifies as inconveniently large, but does its optical design permit it, or are they using that space to make the lens possible?