A data miner named Tero Alhonen claimed he had discovered a new Xbox product code-named "Keystone," which could be similar to the Xbox Series X Enhanced console of Xbox One X.
Judging from the images provided by Tero Alhonen, "Keystone" is listed as a product and is located below "Durango" and "Scarlett", while "Durango" is the code name for Xbox One and "Scarlett" is the code name for Xbox Series X. So what "Keystone" refers to is likely to be a new Xbox product.
Of course, this is all speculative, and we don't quite know what the "Keystone" generation means, but it's located under the development codenames for Xbox Series X and Xbox One, which is very suggestive.
Microsoft isn't announcing any new host devices at the moment, but it's worth considering that console manufacturers typically make plans a few years in advance, so Microsoft may be preparing for new consoles right now.