TLDR: Michael needed to get all 4 of the humans together, but didn't know how. Chidi's idea for the study gave Michael the opportunity he needed to accomplish that.
Earlier in the episode, Michael and Janet are talking.
Michael: "This is not just about Chidi. I've left too much to chance. Until our group is back together again, this whole thing is hanging by a thread. I'm going back down."
Later:
Janet: "How are you even going to get Jason and Tahani to Australia?"
Michael: "I have no idea. But I have to try."
Down on Earth, Chidi storms into Simone's office:
Chidi: "Elanor and I have nothing in common, except that we both almost died, and it made us want to be better people. This is my thesis idea: I will explore the effect of near-death experiences on ethical decision-making. I will get a group of people together who've had near-death experiences, ask them ethical questions, and see if there's any commonalities."
After Chidi's revelation, he posts a flyer on a campus bulletin board. In the background, Michael says, "Bingo! Okay!" with an obvious sense of relief from his anxiety.
So it was Chidi's idea, but it gave Michael a simple way to draw Tahani and Jason to Australia (even though it takes some more machinations on his part to actually get them there).