> There is no guidance whatsoever (ie: Martin Fowler's Rule of Three).
That is completely unfair imo. Although not properly motivated, the advice is all there. "When designing abstractions, do not prematurely couple behaviors that may evolve separately in the longer term." "When in doubt, keep behaviors separate until enough common patterns emerge over time that justify the coupling."
Simplified maxims like "Rule of Three" do more harm than good. Don't couple unrelated concerns is a much higher programming virtue than DRY.