Honestly I really liked River's story line even though my V rejected him; definitely want more from all romance options in general though.
I really think Kerry and Panam each got the "short end of the stick" so-to-speak. Panam's romance line is cascaded into the Aldecaldos general quests as far as I can tell, and Kerry's is just super fucking short, predicated primarily as you letting Johnny control your body for a bit to introduce you to him essentially, and doesn't have enough depth explored to it, even though the end of Kerry's questline is super nice and relevant to the main story of the game.
Basically, Judy is the most developed by far, Panam get's great platonic fleshing-out from the Aldecaldos story but you don't ever get a real date with her, River's story is really interesting but I feel like the game needs more to make his romance option feel fleshed out, and Kerry is tucked away in a corner without enough depth to exploring who he is so much as what he's getting over.
I really hope future updates to the game add more content with all four romanceable characters, and really hope that Panam, River, and Kerry can have a quest that parallels Pyramid Song at least in intent and character depth, though I think matching that quality is gonna be real fuckin hard.