They wouldn’t even necessarily have to start fresh. Berlanti could still be a producer (he produces a TON of stuff beyond CW), could still use Hoechlin, just go outside Berlanti’s usual Arrowverse wheelhouse and spring for bigger talent when hiring the creative team (he already somewhat did this with Black Lighting, even on their same small budget/network). If it’s set during Supes’ early days then they don’t have to worry about much by way of continuity with Supergirl, and just let it be it’s own thing.