If there were going to be chromas, my assumption is that they would have been included in the PBE testing. Dark Cosmic Jhin is also far more advanced than the other skins that were released along side him, featuring a lot of changes to his model among other things, and he's more complex when compared to other legendaries that have chromas. I think giving him chromas would have been difficult due to such extreme changes, and I honestly don't think the skin would have looked good with them. There's also the chance that they just didn't want to give him any.
So, in short, no, I don't think he's getting any.
More important question, though, why did they make chromas for High Noon and not release them?