Content authors should be able to set the date the content should be published

Compared to when Lightning used the Scheduled Updates module, there's a limitation that is not accounting for the very vast majority of use cases for content authoring: content authors should be able to set the date the content should be published and just require that the content reviewer approve it before the scheduling takes effect.

Here's a use case:

1. Carol (Creator) authors a page. She sets its scheduled publication time to Saturday at noon and moves the content to the "In review" state. Problem: The content author can only schedule a transition they have permission to manually perform, so they can't say "this should go live Saturday at noon". They can only schedule it for review at a given time, which nobody does. The fact that there's a specific time at which the content should actually be published would have to be communicated outside the workflow system for a reviewer to schedule–perhaps through revision notes or an email.)
2. Roy (Reviewer) performs editorial review and approves the content. He makes no changes and moves the content to some kind of "Scheduled" state. Problem: There is no "Scheduled" state or any way to distinguish between content that still needs a review and content that has been reviewed and approved but is waiting for an automated publication event.)

With the Scheduled Updates module, content creators could create a scheduled update to publish content despite not having permission to actually perform that transition themselves. E.g. you could create a new "Scheduled" workflow state into which only reviewers could move content. Then you could also create a "Robot" user role that only had permission to move content from "Scheduled" to "Published", and run the Scheduled Updates Drush command on cron using that user. In that way you could give content creators responsibility for defining content publication dates without enabling them to bypass editorial review and we eliminated the need for manual interventions or ad hoc communication. AFAICT it's impossible with Lightning Scheduler.