For me it is Alts
1. Bring my 2nd Account that has been inactive up in rep and story to my main
2. Complete Campaign and Quests with my Alliance Alt
3. Complete the Horde Campaign on my Evil/Loyalist/N'zoth Follower Alt
4. Level up Allied Race Alts
Beyond that just collecting Pets/Toys/Mounts to mix things up.
How about you guys, what do you plan to check off before Shadowlands?