I don't think we'll ever see ninja Reptile again, and I think it's been confirmed that Reptile will become the Dragon King, so he won't be a separate charaacter. Personally I wouldn't want to see ninja Reptile again; closest to it should be a reptillian creature with a ninja-like belt, kinda like in Drahmin's alternate costume. It sucks that he'll be the dragon king though, it's a pretty stupid idea, IMO. I think the Dragon King should have just used Reptile's DNA to replicate himself or something, and left Reptile as is...but further devolved.

I don't think Reptile should further devolve
Maybe Khameleo finds him... and being the fact that Reptile would be with someone of his species would allow him to be more human... Suppose he is the dragon king, that would make the dragon kind more human, meaning he'd look like another Tyrant Shao-Kahn style... I wouldnt mind that... Reptile was cool in MKDA, but honestly, I didn't like his tail...