Walt Disney World is currently running a 4 Fastpass+ Reservations test! The test is running for March 30th and 31st at Magic Kingdom, Animal Kingdom and Hollywood Studios. Currently, you choose 3 Fastpass+ options and it will automatically add a 4th to your list. You can then change the 4th Fastpass+ option to anything that is available after you book what they pre-selected for you.
I hope they decide to give us 4 pre-booked Fastpass+. That would make planning a lot better!