I think they actually retained ownership of all of the top-three settings. So there's one more as well.
Oh, you may be right. Great, then I call for both runners-up to be released.
However, it doesn't follow that they have these settings just sitting ready to be used. The final deliverable from the Setting Search was a 100-page setting bible. This then underwent a lot of development before resulting in the 300-ish page Eberron Campaign Setting book (not to mention the line of supplements). The other two settings, if they still exist, would still be in that raw form.
Still, if the upcoming settings are going to be short-ish PDF releases (like the Magic: The Gathering D&D PDFs), or just chapters in a multi-setting book, then gleaning from a 100-page document is doable. Similarly, the existing settings will need only a certain amount of work to distill and convert them into 5E.
(I also think I saw somewhere that at least some of the ideas from RB's setting did eventually make their way into Eberron. Certainly, WotC may well have picked over those two settings for ideas to use in future books. So there may well not be anything left to publish - just the picked over bones.)
That is possible, but unlikely. Even if a few themes or locales from the other two winners were incorporated into Eberron, surely the original concepts had completely different themes than Eberron. It's unlikely that WotC chose *three* pulp-fantasy settings. And even if there are some shared features, it's not so different than how the Keep on the Borderland and the Tomb of Horrors officially exist in several D&D worlds (Oerth, Toril, Nerath), or how there's a vampire nation named Boldavia in Mystara, which is not so different than Barovia in Ravenloft.
And all that said, there's also a fairly strong incentive for WotC not to publish. The reality is that many D&D players don't use any published settings, and very very few make use of more than one. That means that each additional setting they publish is competing for a slice of an already-small pool of potential customers. Competing against yourselves in that manner doesn't make good business sense.
Dear Customer. Why should we thin out our brand with yet another campaign setting? If you want us to publish it, please drop off $100,000.00 in small bill at the following location.
Jayzus! If I never heard this "truism" again in my life, I'd be happier for it. Ever since Ryan Dancey offered this nugget of wisdom back in 2000, it's been automatically repeated over and over. It was certainly true in regard to TSR's business model, but times have changed. Even Dancey and his immediate successors released (or licensed out) a ton of different settings during the post-TSR 3E era: Eberron, Diablo II, Kingdoms of Kalamar, Warcraft (D&D branded), Wheel of Time, Dragonlance, Blackmoor, Gamma World, and probably others I've forgot. And Hasbro likewise released some settings for 4E: FR (which, if you'll remember, wasn't the core setting in 4E), Eberron, and Dark Sun. All of this happened after that "truism" was well known. Presumably these settings weren't total losses from a business perspective
Even recently, WotC has found a way to make Ravenloft profitable: released as a one-shot, iconic campaign sampler. Even Adventurer's League visited Ravenloft through a world-hopping adventure which leaves from Toril and then comes back to Toril at the end. The same could be done for all the D&D worlds. And 5E has already gone so far as to actually list the names of all the classic worlds in the PHB and DMG, and to give conversion notes for several of the worlds in some of the 5E adventures.
And...one big difference between Paizo and WotC is that WotC does hold a wealth of different settings in its stable, which still possess the power of nostalgia. This is an untapped asset. That's why even WotC's rep recently posted: "people want settings!"
Look - my understanding (and the existing products and teasers affirm it) is that the goal is to present the D&D Multiverse as a unified meta-setting (via Planescape+Spelljammer+Chronomancer), but with Forgotten Realms as the central home base. If Magic: The Gathering can successfully leverage multiple worlds within a meta-setting, then so can D&D. Once you get that meta-setting in place, then the more worlds, the merrier!
So I'd be surprised if we ever saw anything of the runner-up settings... or indeed if we ever saw another new setting from WotC.
Ever, O Delerechio, is a long time.