The positive aspects of suspending speakers are complete mechanical isolation from the floor (so that it doesn't vibrate) and removal of the speaker from all adjacent surfaces. (You would not, for example, put the speaker right next to a side wall).
As to speaker movement...in addition to being a tiny force applied to the massive enclosure, it is at the wrong frequency to induce "swinging". The pendulum frequency of the suspended speakers will be lower than one Hertz, and no loudspeaker goes quite that low. Finally, musicians do not clamp their instruments into rigid mounts as they perform, and neither do audiophiles clamp their heads when listening. The instruments move about at least several inches, so I can't believe that tiny speaker movement is would be a problem.
As always, those who have not tried the idea are on thin ice when commenting. For cosmetic reasons my speakers are not suspended, but I have heard excellent results from suspended setups. In fact, many years ago I heard the original Bose speakers hung about six feet in front of a brick wall in a warehouse with a ceiling of about 20 feet. You would not believe how good they sounded. I have also heard Maggies hung near the middle of a very large room with high ceiling. Also superb.
