Yep, the schedule group action and other related schedule actions are definitely on the roadmap for call flows. We decided to go ahead and release the email functionality first so that customers can take advantage of that for the time being, while we work on adding the same functionality to call flows.
While there are many similarities between call flows and email flows, from an architectural standpoint they use different runtime engines and are implemented a bit differently to a point, hence why the different timelines.
The general guideline is that we want the same functionality across all flow types, where applicable. It may be that some are delivered sooner than others, however.
As far as schedule exclusions go, we are currently working on adding holiday and emergency scheduling into PureCloud and hoping to release that in Q4, which may help with some of the work you are doing.