There is a post function which notifies the overdue as an email. But this notification is only sent after transition happens.
For instance, if you set an SLA from "Open" to "In Progress" and whenever the issue has been set to "In Progress" and there is an overdue according to SLA, the post function will send an email notification.
However, if you want to get an email, before the transition happens, it needs some listener staff. Plugin needs to search all issues according to SLAs with a background task.
This will be a great improvement, and is not feasible according to performancem but I will work on it if you raise an issue
By the way, getting this from the database is really hard. You need to traverse all issue actions and compare the results with SLA definitions. Because there is no additional database table field that comes with plugin. All are calculated custom fields, in which the value is got from the issue actions.