Thus far this season the team has had an off day about every 10 games, or slightly less to be precise. The rest of the season that's about every 7 games, and in September they'll have an extra pen arm. Plus there will be SP options returning to health to be eased in, with any luck. All that to say that I think there will be plenty of rest to go around among the stretched out arms, even if it's not formally a 6 man rotation.
I did want to highlight this though:
I understand the logic here, but I think this misses the forest for the trees. The most impactful thing the Cubs can do to bounce back from a frustrating 2024 is not optimize to get marginally more draft capital, it's to have the players on the roster make improvements and play well the rest of the year. Those two are fundamentally at odds, especially on this roster which has so few potential departing FA of consequence, and the organization is much healthier if Busch doesn't slump, Paredes shows his 2023-24 are repeatable, young pitchers don't hit a wall, etc. You should root for as few questions to answer in the offseason as possible, and while I love min-maxing within the rules as much as anyone and believe the draft capital is underrated in its consequence in general, it still pales compared to the MLB roster being the best versions of themselves heading into next season.