So Lapis is basically aiming to pull a Darkseid on the commoners, manipulating things behind the scenes and even fostering a new beacon of hope that the commoners can rally behind, so when she finally pulls the rug under them, not only the genocide will be justified, it will also cut from the root any future thoughts of insurrection and solidify the Nobles' position.
And yet, I think that final page says more about her mental state, those bags under her eyes and resigned (maybe even wistful) look while she looks at Natori cheering, tells me her resolution is starting to falter and the ominous "I really need to end things" is because she knows that if she doesn't act fast, she will become unable to give up Natori and continue with her schemes.
In that vein, is 100% true that Allie is Lapis' perfect foil and I'm sure that she will be key to stop the genocide and save Lapis from her demise.