Celebi Special Research is here now! You can find the quests under the "Special" research tab and just like Mew, there are 8 groups of tasks to complete. If you have not completed the Mew quest line, don't worry. You only have to complete the third set of tasks for Mew to start working on Celebi. "Johto Festival" Field Research has also been released today. It features many tasks related to 2nd Generation Pokemon.
I will be posting more information as more details for Celebi and Johto Research tasks are released.