Within the far-reaching context of DC Comics continuity, it's certainly a plausible revelation. Grant Morrison's encompassing map of the DCU, as shown in his Multiversity epic, places New Genesis on a plane of existence outside of The Orrery. Clearly, the World Forge also exists beyond The Orrery, collaborating that the Tenth Metal/Element X's origins are on a plane beyond the border of the multiverse. This border, according to Morrison's map, consists of the Speed Force Wall, or the "limit to matter," giving continuity enthusiasts something else to scratch their heads over.
Metal established early on that Nth Metal was harmful to the Dark Knights – Barbatos' assemblage of evil Batmen from various worlds within the Dark Multiverse. The DCU's heroes, then, reasoned that the purer Tenth Metal was the key to defeating the Knights and free the world from its descent into the dark. The Justice League, therefore, armors themselves up in the stuff, and do indeed subsequently succeed in defeating the Dark Knights and saving Earth from being consumed by darkness.
The Justice League Redefines the Multiverse
Hall's journal goes on to reveal more on the exact nature of this fundamental element, calling it "the metal of pure possibility." Regarding those who bear the metal, the journal further states that it can "bring their will to life." This implies that those who wield the substance are akin to gods themselves, which is largely proven out by the JLA's success in freeing the world from the forge of the god who created it.
Here, the JLA doesn't just save the world, though, or even just the multiverse – ultimately, the teams actions end up redefining it. Morrison's Multiversity map ends at the Source Wall, considered to be the limit of existence, but Metal has conclusively established that the Dark Multiverse exists beneath the known multiverse – figuratively, on the other side of the page. What its climax now puts forth is that the map extends to other pages as well – ones that have yet to be laid out, but stand to be explored in the coming years within the pages of DC Comics.
Dark Nights: Metal #6 might reveal that the existence of the Tenth Metal is nothing new, but its capabilities most certainly are.