With FF mirrorless cameras taking over some time soon (I hope
), in-lens IS loses one of it's two advantages over in-body IS: on an EVF, viewfinder image will be stabilized, irrespective of whether IS is implemented in-lens, in-body .. or even in a dual/hybrid way using both. [Second advantage for in-lens IS being the fact that it's specifically tailored to match a specific lens ... and I do not believe this holds much truth any longer against todays in-body IS systems)
So while Canon (and Nikon) had a major advantage with their in-lens IS approach during the (D)SLR era, this is coming to an end.
Personally, I would prefer a Canon FF mirrorless system, of course with new, native, short flange-distance lens mount. Ideally with in-body IS, and lenses without any manual focus gears, only "by-wire" in a really well-implemented fashion. Zoom also "by wire". Either turning rings on lenses or really good, highly ergonomical control points on camera body. Ideally also with non-mechanical aperture ... think of something like a variable, highly transmissive LCD with a perfectly round aperture opening at all openings .. also implemented in body, rather than in evry lens.
To complete my vision of future "solid state" mechanics-free FF-sensored cameras, shutter would be fully electronic.
If the in-body IS could be extended to "6 axis", i.e. adding linear movement in the Z-axis [current 5-axis systems (Oly) allow linear and rotational moves in the X and Y axis and rotational moves around the Z axis] ... then focussing could possibly also take place in the body, without any moving lens elements. With proper lens construction, that is.
This would possibly allow for camera/lens systems with significantly smaller, lighter, simpler, more robust, fully weathersealed, higher IQ [only needs to be adjusted/centered once before leaving factory] lenses ... at significantly lower production cost ... and hopefully prices.
Not sure however, whether I'll live long enough to get it from Canon.
Meanwhile I do expect Canon to come up with in-lens IS in fast primes as well. 50/1.4, 50/1.8, 85/1.8 + 100/2.0 are all very old lens designs and in need of a major overhaul, with the same treatment Canon gave the 24/28/35 IS primes. Not only IS and (corner) sharpness, but also less (lonigtudinal) CAs, please.