Will Jhin be a popular pick?

Yep. I don't see anything wrong with his gameplay - his art direction, yes, but that's another convo. He has very desirable power. I see no reason why he isn't already up there with MF as one of the hardest hitting ranged carries.

He plays a lot differently, but that doesn't necessarily make him bad.

I would say he's probably really good in poke/burst comps. Timing is really important with him since his 4th shot is the one that really counts (on top of him needing to reload) but I would say he'll probably be decent at the very least.

I think he will be more popular than Kindred and Illaoi and the other recent champs because he is a sniper and lots of gamers love their snipers. Seriously lol. He will be popular because sniping is just cool. Also the music is pretty badass during the ult and makes you feel like you are the sniper yourself in a way.