Wow, I can't believe it's been 2 years since Pop. I'm Nayeon is one of my favourite k-pop EPs so I'm super excited to see what she does next.
I def agree that it was the right timing. Giving Nayeon anything other than a spring/summer release would be dumb and furthering her public persona in this way makes the most sense and it makes sense for Twice. I personally hope it's as fun and whimsy as Pop was, but I wouldn't be opposed to it being a "cool" bop instead.
As for Twice, they're not going anywhere but for people who aren't sold on them or have fallen off, Nayeon could def help bridge the gap. She also personofies a lot of the favourite hits from Twice (Fancy and Feel Special feel Nayeon/Sana coded to me, as non-once but that could just be me being superficial).
Regardless, I'm excited and I hope JYP got her good music (and that Nayeon was able to participate in the creation as much as she wanted)!