Arcade Fire has been playing Reflektor pretty early in their set on tour so far. If they don't play it within the first 3 songs at Coachella, good possibly that they're saving the song for a Bowie guest spot on the song? Followed by Heroes/Life on Mars/Changes/Fame (god please)/etc.etc.etc. Ending with Wake Up.
I have a sense that Childish may make an appearance for both Weekend 1 and 2 of Coachella. Checked his tour dates and those two weeks are empty. Plus, he featured in songs with Chance the Rapper and Jhené Aiko, who are both performing at this year's festival. Just saying it could be a possibility.
Possibly for weekend 1 but he has a concert in Hawaii on the 19th meaning that he may not come on weekend 2.