The following article contains spoilers from Flashpoint Beyond #6, on sale now from DC Comics.
The ending of Flashpoint Beyond #6 (by Geoff Johns, Tim Sheridan, Jeremy Adams, Xermanico, Mikel Janin, Gary Frank, Romulo Fajardo Jr., Jordie Bellaire, Brad Anderson, and Rob Leigh) saw some major changes to the history of the DC Universe. Rip Hunter wasn't just trying to prevent the Flashpoint timeline from integrating into DC's history, he was also trying to stop thirteen individuals from rejoining the true timeline. One of those individuals is someone known only as "The Golden Age Red Lantern"
This changes a massive amount of lore in the DC Universe. Up until now, Atrocitus was the first Red Lantern to exist, his rage having created the Red Lantern power battery. Yet, this new addition to the timeline suggests that this was never meant to be the case and that another person originated the Red Lantern Corps. This has a lot of implications for the Green Lantern of the Golden Age, Alan Scott, and the current balance of power in the present-day DCU.
The Origin of the Red Lantern Corps
The Red Lantern Corps was initially born from Atrocitus' rage. One of the five survivors of Sector 666; Atrocitus was imprisoned shortly after, his rage helping to create his corps' power battery. This, however, would have occurred well after the Golden Age, just before Abin Sur passed his ring on to Hal Jordan. So while it is in the past, it is not the distant past.
The introduction of a Red Lantern Corps during those days suggests that this was always meant to be and that perhaps the Red Lantern Corps was supposed to get its start back then. If so, then whoever this Golden Age Red Lantern is, they may be the true originator of the Corps, a being so empowered by rage that it fundamentally altered the balance of power in the universe. It may also shine a light on the origins of the Butcher; the entity of rage in the DC Universe.
How a Golden Age Red Lantern Affects the Green Lanterns
The immediate threat is against Alan Scott. Though he operates under the name "Green Lantern" he is not actually a member of the Green Lantern Corps. In fact, his ring is more magically empowered than scientific. He is truly one of a kind, and as such stands alone against the coming threat that is now integrating itself back into his timeline. A Golden Age Red Lantern will most likely target him at some point, or even worse, might sic the entirely new Corps on him.
Then there is the overall threat this new lantern potentially poses. The Time Masters thought it was necessary to remove this person from the timeline. This wasn't some aberration, this is what was meant to happen, and it was dangerous enough that it had to be removed. It suggests that the Golden Age Red Lantern did indeed expand their new Corps. While people look back on the Golden Age fondly, were full of people who could be empowered by rage. If so, then the present-day Red Lantern Corps might expand into an army, unlike anything the other corps have seen before.