It has been revealed that some merchandise for Zack Snyder's Justice League will include references to the Green Lantern Corps with their insignia appearing in a sticker pack. Of course, even in the 2017 theatrical cut, one Lantern did make a brief appearance during the history lesson scene. However, beyond that, fans only have jokes made by Ryan Reynolds of himself appearing as Hal Jordan in the Snyder Cut.
On the other hand, it has been widely reported that Harry Lennix, who previously played General Swanwick in both Man of Steel and Batman v Superman: Dawn of Justice, will be revealed to have been superhero Martian Manhunter all along. Lennix even went as far as to confirm that he filmed for this character in the Snyder Cut, although he admitted that there wasn't much to film.
Although, it was probably enough for a cameo...
A SUPERHERO CAMEO FOR “HARDCORE” FANS
A recent report from Vanity Fair about Zack Snyder's Justice League mentions that the DCEU director has re-shot the ending, including a cameo that will supposedly "blow hard-core fans' minds."
CAMEO IS LIKELY EITHER MANHUNTER OR GUARDIAN
The only two likely possibilities for this superhero cameo are J'onn J'onzz, a.k.a Martian Manhunter, or one of the more iconic Green Lanterns like Hal Jordan or John Stewart. At the moment, there is a lot more evidence of this hero being Manhunter. Zack Snyder has already teased a quote from Manhunter that heavily suggests that it's from the movie's ending, hinting at the war with Darkseid.
While there is indeed merchandise with the Green Lantern insignia, that isn't enough proof to point to this cameo being Jordan or some other popular hero from the Green Lantern Corps. However, it would certainly surprise hardcore fans, considering most of them who have been following the news of the Snyder Cut shouldn't be too surprised by the appearance of J'onn J'onzz.
It will be interesting to see if this movie will actually end on a cliffhanger that may never be resolved, especially since it seems like a continuation may only happen now in the form of a comic, which itself might not even happen.