I start to buzz with enthusiasm the moment either js or jh mentions anything related to the unit. I don't have many data points to draw a concrete analysis so this is purely what I think and my own drawn conclusion.
I'll start with Jeonghan. when you dive into Jeonghan's vocal journey through his solos, his ideas, his vision when it comes to music become really vivid. I'll die on his hill but jeonghan is a yearner through and through. his first solos, like dream and coincidence give a strong acoustic/soft ballad type of vibe esp coincidence have crazy potential to be an OST. Jeonghan's vocals vary from acoustic, R&B(purple rose, beautiful monster (kinda lies in medium tempo), soft ballad, and indie pop. So, there's a lot to experiment with.
Now, when you talk about Joshua's solos-- fortunate change is like a holy grail for me. if anyone in svt I think Joshua has the best vocals when it comes to acoustic songs. he has the perfect voice for it. so, the genres his vocals vary from are acoustic, soft ballad, R&B (double take cover, and kids are born star), indie pop(?) I think. much similar to jh (one of my reasons why I think this unit just makes sense)
so when you talk about them singing together-- falling for U is a great (and only) example to follow. it gives off sorta jazzy and chill pop vibes.
I think they'll for sure explore more of R&B. I mean, this is what I expect. Given both js and jh are working on the lyrics as well, I'll be sure to expect some sad, yearning ballads as well. I might be aiming for the stars with this one but I REALLY hope that the album has some solos as well and jeonghan does something j-pop related bc I need a sibling for better half. and for js to have something mandopop ballad. anonie if either of these things happens, I will end it for sure. so, this is where my expectations lies. well, at the end of the day, I know I'll be fed well.