If you look at what happens to muscle mass with bed rest--somebody with complete bed rest will lose a substantial amount of muscle, compared to, say, somebody who is standing for just an hour a day. People in other cultures are more comfortable squatting than we are, and they do a large amount of bodyweight squatting. But with exercise, there's generally a point where you get diminishing returns--you are adapted to the stress to the point where increasing the duration of the exercise doesn't yield a training effect.

If the problem with sitting in chairs is deloading, I think finding the effective dose of not sitting is relevant--and an easier and more likely sell. I sort of doubt that chairs and sofas are going away. Getting in trouble with blood clotting etc. is another story, but there there's also the question of what makes somebody prone to that, is the problem that sitting in chairs for long periods of time is something that human beings are not adapted to, or is the problem that what we do when we're not sitting in chairs, and what we eat whether we're sitting in chairs or not, etc., has compromised our tolerance for what chair sitting we do do?