So many responses that missed the point of my question -- which was not about the benefits of stabilization, but the benefit of in-body versus in-lens.
Working backwards:
Stevelee: I'm not familiar with the 6DII, but I think you are referring to the cropping of video to stabilize a scene, as can be done with Premiere Pro. That's actually a good argument in favor of 4K, which allows video shooters to crop and still retain a full HD image. I was aware that Canon's 18-135 EF-S lens has something they call Dynamic Image Stabilization to improve video performance, but was not aware that Canon used in-lens stabilization systems with specific cameras in conjunction with video, but that's a nice feature, although it's not relevant to IBIS.
Mt. Spokane: Good point about fast primes. Might be relevant to others, but I'm not a fast prime user, so doesn't apply to me. However, it certainly may apply to others.
Don Haines: I had not heard that rule of thumb regarding telephotos vs. wide angles. I'm curious what the reasons might be for the difference.
Amorse and Adelino: I can see where it would be nice as a way to essentially add stabilization to an expensive Canon lens like the 24-70. I don't think of that as an inherent benefit of IBIS, but rather as sort of an after-market solution for the manufacturer's failure to include it in the original.
Photo Hack: Your response is not clear.Maybe you are referring to the feature that Stevelee references.
YouengLinger: Most of your answer (if you were responding to me) seems to be about the benefits of IS generally. Also, I'm not sure who you think is "repeating the myth that it doesn't help unless the subject is completely still." That's certainly not what I said. In my experience, modern lens IS is good enough to allow handholding down to somewhere around 1/4 to 1/2 second. If you pick your shots carefully, you can catch a speaker during a pause, but when you get down in that range, is does get very difficult to get a sharp image of a person. Still, how is that going to be different with in-body stabilization?
What puzzles me is why members of CR who seem to genuinely enjoy Canon products get so nervous (for lack of a stronger description) about IBIS. Are you afraid Canon will botch it so badly it makes your pictures worse? Or that it will fail a few days after the warranty period? That it can't be disabled if you hate it? Just kind of odd that some of those who routinely defend Canon have so little faith the company can reliably implement IBIS.
For now and the foreseeable future, Canon offers bodies without IBIS. In what way will a new body with IBIS affect your photography? Why fret about it?
This portion of your post is truly perplexing. Who has ever said they were nervous about IBIS? And, who has ever said they don't think Canon can implement it. I've never read any post to that effect. Some people are concerned about the durability of IBIS, but I assume that before Canon introduces it, they will stress test it. The only concern that I stated was a very vague one that I was overlooking something that would cause me to regret purchasing a body without IBIS, if Canon releases one with IBIS.
So far, none of the answers to my question have given me cause for concern. I haven't found anything in these many answers that makes me feel that IBIS is so useful that I would have buyer's remorse for purchasing a body without IBIS.
Kit: You make a valid point. I'm not a lens designer, but it certainly does seem logical to me that some lens designs would be better served by in-body stabilization.
I've already responded to
Keith Cooper and he makes valid points.
Quarkcharmed: I'm not questioning the value of IS in general. I use it routinely. Question was about the value of in-body over in-lens.
Apologies if I've missed or offended anyone.