This feels a little overblown to me, like Gelb thought he had a fun idea for a column and Kapler is willing to consider anything. Maybe they'll carry nine relievers occasionally, but the shorter bench, and the machinations involved to shuttle guys back and forth (including a position player when you wanted four, or during interleague), would get a little out of hand.
Plus the key phrase is in the headline - "absent a rotation addition." The beat writers have chosen to take Klentak and MacPhail at face value, partly because if they don't, that means they are failing to get any information about what might really be going on.
I don't really mind the analytical approach or the ostensible plan to give all these young arms a shot, but not letting your starters go three times around an order only works if they are effective the first two times. If they're only going four innings in that scenario, a better bullpen's not the fix.