Omega is also working for NJPW under the DDT banner. The only wrestler I know that has recently signed on from another company to NJPW is BUSHI from All Japan.
As for Naito, he was getting built to make a push for a title shot before he got hurt earlier this year, but that delayed his plans. Naito can perform, but I don't see Okada dropping the belt to him, mainly because I think Naito's a bit away from being the main champ.