Forget about deep discounts on last year's models. I made the mistake of thinking I could get a 2017 cheap. Nope, bought a 2018 (after careful shopping) for far less than I could have bought a 2017 in January. Seems bizarre, but I did a lot of frustrating shopping. And the 2018 had improved tech LKAS. More supply means better pricing versus marketing hype on closeouts (lies). The exception is when closeouts have a huge supply on a mainstream car, then you can get a good deal.
For 2019, there won't be a lot of changes. Possibly an auto dim headlight (who cares?). More substantial could be headlight upgrades, like LED or HID in lower trims. The major change is likely to be an inclusion of the tech package into some trim levels without paying for it as an option - assuming they do what Hyundai has already announced for 2019 models - likely. That may or may not improve the value proposition of the 2019 depending on what trim level you will want versus trim level in the 2018. I wouldn't bother waiting on the HEV, but if you want the PHEV, prices can only drop next year if supply increases. I doubt if anyone is snagging a significant discount (or any discount) on the very few 2018 PHEVs available. Not sure if they are even making more.
2018 Kia LX HEV Metal Stream with Advanced Tech