WDW removed park hopping restrictions for all ticket types that allow park hopping. The only thing now that could prevent park hopping is capacity. If that happens, it affects all ticket types.
AP holders can park hop to the MK after entering any other theme park first (a park reservation for your first park may be required).
AP holders can enter Epcot, DAK or DHS after 2 pm any day of the week without a park reservation.
AP holders can enter the MK on weekdays after 2 pm without a park reservation. On weekends, if the MK if your first park of the day, AP holders will need a MK park reservation regardless of time.