I definitely think pop MUSICIANS will come back; but if you're looking for suggestive danceclub 2009-2015 pop I doubt we'll see that for another few years at best. I feel like a lot of it will be centered around lyrical content and experimental/genre hopping production. Groups like LSD and girls like Charli XCX I genuinely believe are some of the first to take hold of what pop music will veer into during 2019.
I can see Demi going much harder into RnB, same with Ariana. Selena will probably stay as experimental as Bad Liar was if she knows what's good for her, Beyonce & Rihanna I feel will have a multitude of sounds like their 2016 records, but stay urban and have a sense of identity away from 'pop' as a whole.