RGBZ in general. They killed a market just to have a minor feature in their phones. Also keep in mind that Primesense's biggest precious licensee was an Apple competitor.

They’re adding rear facing depth sensor for use with ARKit and are known to have an AR headset in development. I think the new sensor works differently from Primesense (which used a grid projector and a camera instead of LiDAR?) but clearly Apple is doing more with this. I'd be shocked if they didn't have years worth of prototype phones with Primesense systems on the back.

Unfortunately this is still a very narrow vision of what is possible with RGBZ or just Z. You won't want to strap an iPad to a robot, or mount a bunch of iPads on your ceiling, or below your TV connected to your game console.