I am much more explicitly not doing much of anything with the lands beyond Khorvaire, but since there's a section in the Setting Book that covers it, I'll mention it briefly too. In general, I don't much care what's beyond Khorvaire too much, other than it may be the source of threats in Khorvaire. I might eventually have some sojourning on Xen'drik happen, since that was certainly an expectation of Eberron as written, but I'm actually indifferent to the idea myself, thinking that Khorvaire itself is sufficient and more than sufficient for any campaign I could concievably run. Because of that, rather than remixing much beyond Khorvaire, other than applying the same general principles of the remixing of the entire setting in a broad, handwavy fashion, I don't intend to do much. I'll extremely briefly address the various subheadings in the section, however.
Aerenal: The Undying vs. the Undead is too esoterically D&D to make any sense to me, honestly. The whole "no, no—it's positive energy rather than negative energy" was always rather silly; these are just really spooky seraphim with a civilization that one-ups ancient Aegypt in terms of venerating and preserving the dead. It's kind of a moot point; the Aerenal folk are rather isolationist and unwelcoming, so it's more a point of reference than a place to visit. If I ever need anything from here, I'd refer more to ancient Nehekhara from Warhammer as a point of reference than the rather sparse stuff detailed here, and make them considerably more creepy and sinister. But I doubt I'd bother spending too much time with that.
Argonessen: This continent is so disconnected from almost anything going on in Eberron that I'm not even sure that it exists in Eberron Remixed. It might not, because taking it away changes almost nothing at all about the setting anyway.
Frostfell: There is so little detail about this polar continent that I might as well ignore it too, other than that it is—or was—the original home of the Hyperboreans, and Zobna was in the interior, and Lomar perhaps on islands like Farlnen that are now mostly uninhabited, yet occasionally prowled by the northernmost Lhazaar pirates. But even that is just a point of reference. I doubt I'd ever have anyone go to even those northern islands, much less the frozen continent beyond.
Khyber: I did mention this a bit in the Magic section, but given that this is such an incredibly iconic D&Dism, it doesn't seem to make sense to continue to use it when I'm deliberately avoiding the D&D-specific stuff. I'll almost certainly ignore this as much as feasible.
Sarlona: The main setting book says very little about this, actually. Of course, I've read Secrets of Sarlona, but the reality is that this continent isn't really designed for very easy use. I'm going to mostly ignore it except as a point of reference, and I also don't intend to use the Dreaming Dark as a significant threat. I'm not going to write them out exactly, I'm just going to mostly ignore them.
Xen'drik: I've never really understood why the position of Xen'drik (from a metagame) perspective was really developed, or maybe I'm just stubborn and refuse to believe that having a separate continent of "monsters and dungeons" really made sense to anyone at all. I'm not all that interested in Xen'drik, but it does lend itself to being used somewhat more than the other "beyond Khorvaire" areas, and many modules and novels and more at least partially take place here. I'd see it more as a primitive "Scramble for Africa" situation with colonial powers just barely getting a toehold on the continent, than anything else. As elsewhere, rather than being populated by tons of giants, I see the ettins as being rare, and savage humans being the most common inhabitants, followed by kemlings. I do think wild magic hazards might explain the reticence of anyone to seriously try and set up permanently here, though, so maybe I'll keep some of that vibe. In addition, although primitive, and in some ways analogous to late 1800s Africans from a social perspective, the natives of Xen'drik are much more dangerous and unfriendly than any of the Africans were, making it require full-on military invasion to really make any headway in exploiting Xen'drik, and with more pressing matters going on in Khorvaire, nobody has seriously considered that at all.
History of the World: I'm not going to address this timeline. I've had some stuff here and there which contradicts some details, but ultimately, I don't think histories stretching tens of thousands of years back is very interesting or relevant, and I've gradually come to see it as a weird affectation that fantasy fans would do better to let go of. I suppose anything that isn't explicitly contradicted in this history can be assumed to be more or less correct, albeit completely irrelevant unless it's of pretty recent vintage anyway.