With Hunter X Hunter on the block, Toonami is going to be inevitably acquiring less shows than it has been anyway. Making the likely assumption that Toonami is getting Buu Kai, and also assuming the rerun slot stays, that's only 2 rotating shows for a while. Not to mention Samurai Jack has to fit in somewhere.
There really was no doubt One Punch Man was going to air at some point, due to its popularity/appeal and, well, the type of show it is. From my perspective as a plebeian casual, stuff like Kabaneri or Ushio&Tora are not nearly as prevalent in general mind-share and I'd say their chances are much more in doubt (but not impossible, obviously).