I guess I'm not a real boater. For me, packrafts opened up the boating thing by packing small and being light. I'd not have a boat at all if it weren't for that.
Seems like the limits of the boats are still being explored. Videos like this might help to start answering your questions.
Spray skirts, whitewater decks, knee straps, back bands, cargo fly… Some mods people are making for whitewater are available from Alpacka. Many of the mods are DIY based on perceived needs of the paddlers. I've seen some prototype boats that are further blurring the line between inflatable raft and hardshell.
My wild guess is that one should probably spend less time trying to make a packraft into a kayak. Instead one should explore the genre for its own merits. Packable. Capable.
Notes from my limited experience: Packrafts are more stable, less "carve-able", more buoyant. Rolling takes a modified technique and is a bit harder due to the stability. (Kayak guys can't seem to jump in one and roll it immediately.) Cargo fly equipped rafts have amazing capacity for multi-day gear. (I've had 6 days of crap loaded in mine.) My packraft has encouraged me to go where I wouldn't have gone before.
Definitely a great way to mess around in boats!