Dark Sun 5e
Mike Mearls admitted that WotC and the D&D team have been working on Dark Sun for 5th Edition!!!
The main issue they have been working over is Psionics, which is crucial for Dark Sun. He also admitted that once they figure out Psionics, other IP’s are likely to be worked on that also have Psionic elements!!
Source: The Mike Mearls Happy Fun Hour, 5/1/18. Co-creator of D&D 5th edition Mike Mearls shares his process of RPG design. In this episode, Mike dives into Psionics.