It can also depend on how FFG decides to define "era."
It may well be that their definition isn't so much "books set in a specific time frame" but rather "books that are applicable to all three product lines instead of just being specific to one of them."
As for the books under the default definition of "era," thus far the three books we've gotten (Dawn of Rebellion, Rise of the Separatists, and Collapse of the Republic) have only covered a very short span of years. So it's entirely possibly that for the sequel era, they could go the same route they did in covering the Clone Wars and split it into two books, one focusing mostly on the years leading up to and up through Episode 8 (given that TFA and TLJ happen pretty much concurrently) and thus setting the stage by detailing the New Republic and state of galactic affairs before the First Order came in and started kicking the ant-hills, with a subsequent book covering the years in between 8 and 9 with perhaps some hints as to what happens after the Skywalker Saga comes to a close.