Hi, Keith! It's been a long time. (You first knew me as Jhonen Olain, though I prefer my "official" Eberron name of Jani Onyll).
I'll admit that my interest in D&D waned during 4e, and that Eberron never felt as at home in that edition. Maybe it's just my perspective, but Eberron always felt like the ultimate expression of 3rd edition D&D, a setting in which every 3.5 mechanical quirk had an in-world explanation.
That said, I like what I've seen of 5e and I'd love to see Eberron make a triumphant return in the edition. To answer the question, I don't think much is gained from a move forward. If you change enough to warrant all-new setting books, you run the risk of it no longer feeling like the same setting. And of course you run the risk of telling people that the events of their own campaigns were "wrong."
A move backward is much less controversial, and one viable option is to create a single Eberron book called "Eberron: the Last War." The Last War is the second-most-common time period of Eberron games I've seen, and all the crunch for that time period is still relevant to 998 YK games. The notion of a wartime setting is also one that could hook a lot of people, even those unfamiliar with the setting. For anyone who wants to play after the war, the setting fluff is still widely available (and things like maps of pre-Mourning Cyre could be good inspiration for post-Mourning dungeons).
But I think the absolutely ideal way to to do Eberron in a new edition would be to stick with 998 YK and use a very successful format that WotC did not fully leverage in 4e: an adventure path. Eberron has so many flavorful locations that I think the best way to experience the world is to hop from highlight to highlight, rather than immersing yourself in one specific region. A single adventure path could give players exposure to the unique and iconic elements of Eberron: the towers of Sharn, the once-mighty goblins of Dhakaan, the Undying elves of Aerenal, the dragons of Aronnessen, the pragmatic use of undead in Karrnath, the fanatacism of Thrane, the giant ruins of Xen'drik -- all delivered as encounters rather than descriptions.
It might take two books. I love the idea that has seemed most popular in this thread: a book on Eberron player options that includes "modules" for artifice, airships, dragonmarks, and living constructs. Release it alongside one mega-adventure hardcover, and I think you have the dream scenario.
Whatever you do, just make sure you've got Steve Prescott leading the art team.

I believe he's as crucial to the feel of the setting as Elmore was to Dragonlance and DiTerlizzi was to Planescape.