Hi,
No, this is not possible in DSpace 7.x. Embargos are just "start dates" to a permission. So, when you say that an Item should not be publicly accessible until Jan 1, 2025 (i.e. an embargo until that date), that creates an "Anonymous READ" policy that will not begin until Jan 1, 2025. So, prior to that date, the policy is inactive and it becomes active only when the date passes. There are no notifications sent out when that date passes, and no changes made to the object on the embargo expires.
The only way I can think of to do this would be to create a custom script which checks all policies which recently began (start date = yesterday) and send notifications based on that. This isn't something DSpace can do at this time, so you'd have to write custom code to achieve this.
Tim