I'm thinking now that the target area idea I proposed could have the modifiers "target reset" and "cycle reset" (the latter solving what's being discussed).
Without modifiers, area targeting resources would make the selected units first focus on them, and continue gathering the same resource around, as usual.
With the "target reset" modifier, only the resources inside the selected area are targeted, nothing outside it.
With the "cycle reset" modifier, the selected gatherer randomly chooses between the targeted resources after reaching a dropsite.
Some of these would have uses in combat also, for example when selecting ranged units and area targeting some enemy units with the "cycle reset" modifier, each missile would be aimed at a random targeted unit, acting as an "aim at will" command to homogeneously weakening them, instead of attacking some unit until it dies and then switching.