I read a discussion on Mike Holt’s forum once where someone said the 2002 code actually required the handle tie when outlets were on the multi wire branch circuits. The 2008 code then included devices and equipment as part of the handle tie requirement.
The question is, what is your definition of “equipment on the same yoke?” I generally define “yoke” as a device or piece of equipment contained in a single “space” or enclosure - such as a multi-wire circuit powering a single duplex receptacle.
My interpretation is that there is no need for a handle tie in the instance I described, as these are not “on the same yoke.”
That is consistent with the way that I have always treated it. If they are connected separately to a single duplex receptacle or stacked switches on the same yoke - yes; separate outlets and switches - no. I consider whether someone can safely work on one circuit and not be endangered by the other. Though the shared grounded conductor may present a potential issue.
All multi-wire branch circuits require simultaneous disconnect (multi-pole CB or handle tie) under the 2008 NEC. This requirement was actually in the 2005 NEC {605.7} but only applied to freestanding type furniture partitions, and as mentioned MWBC’s on the same yoke.