It's been a code requirement for as long as I can remember. Do you know when it first appeared?
If we mean truly separate circuits, it is not that long ago. It first appeared in 2002.
210.7(C) When more than one branch circuit supplies more than one receptacle on the same yoke, a means to simultaneously disconnect the ungrounded conductors supplying those receptacles shall be provided at the panelboard where the branch circuits originated.
If we talk about one multi-wire branch circuit, is goes back to 1981.
210.4 . . . In dwelling units a multiwire branch circuit supplying more than one receptacle on the same yoke shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit orignated.
In 2005 they took out the reference to dwelling units.
Edit: I think I missed a page . . . looks like it's covered.