There are still quite a few planar creatures left out there that need to be updated. WotC loves their modrons, and there are still ten types of hierarch modrons left to detail. Demodands/Gehreleths have been in pretty much every edition since 1st, and haven't appeared yet. And we have stats for most of the Demon Princes, but very few Archdevils yet. And the celestials have been criminally neglected this edition, although they are already hinting from the species being tested in One D&D that they're already working on that (so introducing more of them in Planescape this year would make sense).