While it is highly unlikely that we will be seeing a "slim edition" of the Xbox Series X any time soon, it is being reported that Microsoft may be developing a smaller, more power-efficient chip for its ninth generation powerhouse console.
It should be noted that Microsoft is constantly developing revisions of such components, and information on this supposed chip revision for the Series X remains scant at this point. The source of the speculation comes from a new video from gaming journalist and insider Brad Sams, who is also Vice President and General Manager of Stardock Software. In the video Sams states (in around the 25 minute mark) that he is "very confident" that the Series X will see a revised chip in the not-too-distant future.
Such hardware revisions are commonplace, and indeed par for the course for most consoles. A smaller, more efficient chip would reduce production costs for Microsoft, as well as help in Microsoft's Cloud Gaming data centers, so it really seems like a foregone conclusion that Microsoft would eventually do such a revision.