This is a chapter that is heavy on mechanics, none of which I need to reproduce here, but there are a few setting related details that are worth discussion. In particular, it talks about the Dragonmarks. I've added a small section to emulate rules set for Dragonmarks, but I mostly just refer you to the Eberron mechanics if you need them. I don't envision that most players will take Dragonmarks or that mechanics will really ever be needed, and that Dragonmarks are more of a plot device than something that needs mechanical expression. But if someone really wants to do so, they can utilize the actual d20 Eberron rules and run them alongside the m20 rules just fine. In fact, that's one of the big advantages of m20; that you can run a d20 subsystem if desired and needed without any real conversion needed. I guess I also kind of give away my opinion on the Dragonmarked Houses and their particular brand of magic too; I simply don't see them as something that a player character is likely to need or want or that a GM is likely to need or want, so I don't want to put much effort into converting them, and I prefer to keep them more as patrons for intrigue and whatnot rather than expect that player characters are running around using their magical mark of sentinel to cast protection from energy once a day or whatever.
Other than that, the chapter also refers to some minor changes to some skills and spells, notably the idea that Warforged need "special" healing (repair) and healing magic because they are constructs, not normal healing. I've decided that this is too fiddly and mechanical and I don't want to mess with it. Being a living construct means being alive, therefore regular healing works the same for these characters as for anyone else.
The final section in this chapter, which does merit a more significant discussion is religion in Eberron, and I will be remixing this significantly. Because there are no clerics or paladins, I doubt that religion will play a major role in any Eberron Remixed campaign—in my experience, really only clerics care much about religion, other than the dangerous cults and evil followers of dark gods or whatever that the PCs oppose. I also tend to be unhappy with the tendency of a lot of settings and gamers alike to try to hash out real work social statements with regards to their religion that I don't really want to hear. So, I've decided to kind of handwave the whole thing away to a certain extent. There are a number of religions listed, and I'm going to go through them all and discuss what I've decided to do about them.
The Silver Flame. This is the obvious stand-in for Christianity. Except that it goes out of its way to talk about its frequent intolerance, and of course, the Christ-figure stand-in of sorts was a little girl. (I'm actually not kidding.) So... it reads like an atheist and SJW's attempt to mimic Christianity, yet still make it something that isn't too off-putting to actual Christian players who will read it. Blegh. I'm just going to go ahead and assume that the Silver Flame is Christianity completely and utterly. With all of the stuff that that means. However, because I'm an American, it's going to be more American style Christianity; decentralized, localized pastors and their churches, not big, centralized Vaticans and whatnot. This does also mean that significant differences will be mandated down the line when I get to describing Thrane, but that's OK. In fact, those differences are probably not going to go the direction that you thought, though.
The Sovereign Host. I do admit that for many years I thought a pagan pantheon of deities went hand in hand with D&D and D&D-like fantasy, however, again—without clerics I don't really know that I see the point anymore. I suppose that I would see the members of the Sovereign Host as somewhat more like patron saints who's probable root was in pagan religions rather than historicity, but all that means is that people will pepper their speech with references to them from time to time; hardly an important or significant element of the setting anymore.
The Dark Six. I see these as more or less the way that they are. Often referred to as the Fallen Saints, they get referred to mainly in curses and epithets. But again, they're not the subjects of a religion in its own right, with the odd exception of some zealous cultist or eccentric heretic or whatever.
The Blood of Vol. This is pretty much exactly as stated; an evil cult of undead-loving necromancers. Not expected that any player characters would join an evil cult, really, but I guess I could see a situation where an evil cultist was a PC for some reason.
The Cults of the Dragon Below. This is an unusual Eberronism. The Dragon Below, or Khyber, is mythologically one of three creator dragons; a collection of Ymir figures if you will that form the basis for the world itself from their bodies. In this sense, Khyber represents the Underdark and the monstrosities that come up out of it. Given that my own ruleset is deliberately kind of Lovecraftian, including many of the monster selections, I think reskinning this to be less Eberron specific in this regard and more Lovecraftian actually works a little better and avoids unnecessary redundancy. In fact, I'd rather completely replace this with the Dark Tapestry cults or something very much like it from Golarion, which is a great iteration of what a Lovecraftian cult would look like in a D&D world.
The Path of Light. Referring to the philosophy/religion of the kalashtar of Adar. I don't know that I care much about this "religion" or have ever really heard it referred to much in most of the Eberron material I've read in the past, but I think it's fine, since it represents an obviously miniscule foreign intrusion into Khorvaire and doesn't play much of a role in anything. The same is true of...
The Undying Court. The idea of "undead, but good, not evil!" is kind of silly, and one that I've never really gotten into. I can accept the idea of some kind of bizarre ancestor worship that goes that far into genuine creepiness not being an actual and total abomination, but again, this is just a really weird, creepy foreign cult that have little to no application to life on Khorvaire anyway.
Anyway, I know that there are some other cults that belong to the setting, but I can't remember off hand; I'll probably get to them as I continue to go through the book analyzing what needs to be remixed when I get to Organizations. I'm not quite sure why the Blood of Vol and the Cults of the Dragon Below weren't listed there too. Was Keith Baker assuming that PCs might want to join the Cults of the Dragon Below or the Blood of Vol?