Green open access and rights retention (i.e. the rightsholder applying a CC BY license to the accepted manuscript prior to licensing the publisher) were zero-cost to the author options for open access, which are part of a sustainable transition away from subscription-based models. ACS have set a precedent for charging for this option, they have not increased the options available to authors.

It's unclear what the subscription costs for the same works are covering if this is the purpose of the ADC.

"new [paid] option". Copyright owners can assign whichever license they choose to their works. If a CC BY license is applied to authors originals or the accepted manuscript arising from a submission, prior to signing away any of these rights, a zero-embargo green open access option was already available. This option is for the author to license the publisher to charge them a fee. The cost and the licensing requirements asserted by the publisher may become a barrier to rightsholders engaging in an activity they previously had an option to engage with.