I doubt the GX will get a 4 cylinder. Plus there are no GX500H trademark to my knowledge, only GX550.I can sit here and imagine what I want, but the 3rd gen GX's [insert favorite word]gate is already a done deal. I do wonder if Lexus's will do more (pains me to say this) "LRD" versions.
The LC300 had a diverse variety of trim levels and while they had their weird caveats (why are rear lockers only available on the GR) I'm wondering whether that will be something GX product planners bring to table. Its been their new strategy to appeal to more price points in every model launch thus far.
I also do wonder if @ssun30 predictions on a 500h powertrain being brought upto the 550. Interesting to say the least.