A few years back, I could have believed in a 6E for 2024, but not anymore. 5E is going way too strong for them to consider a 6E at this point, and to put out a 6E at this exact time, they'd have to start working on it pretty much now. I expect two things, one likely, one less so.
A revised PHB, but not a 5.5E. Like in 2E AD&D, a minor revision that is fully compatible with the earlier printings. Largely it will be a cleaned up version of the existing rules from the RAI sage advice answers. It will include some things from later books deemed worthy of inclusion into the PHB. Any revisions would be to improve existing things that are sub-par, not to nerf things as was largely done with 3.5E. New design and art, of course, for those interested in such things. While the most interesting item, I suspect this isn't exceptionally likely.
A History of D&D, giving an overall view of the game from conception in the early 70s to today's 5E. Comparisons between the various edition, a discussion of the campaign settings, notable content providers (especially a memorandum of those who have passed), and other similar type things. Photos of behind the scenes at WotC, TSR, and possibly even the original days with Gygax and Arnson (if the estates are willing to allow them). This is by far the most likely product, even if not quite as I've described.