For those who might not know, you get shiny Diancie on step 8/10 of its Masterwork Research.

Yep, you just need to get to part 8/10 to get the shiny Diancie. Part 9/10 rewards you with 300 Mega Diancie energies after you win 6 mega raid battles and catch a Pokémon on 21 different days. I don’t think anyone knows what part 10/10 is yet (probably participation rewards if I had to guess).