1. Obvious bias towards Shanks and his motivations. The CD stuff is getting closer but we stipl dont know what he actually wants with Luffy, nor his true relationships with other antagonists like the Gorosei.
2. Blackbeard definitely next. Why cant he sleep? Whats up with his body? Does he have a 3rd fruit? How is he transferring DFs from one person to another? Im not sure how deep motivations go outside of world domination but the above makes him very interesting
3. Imu next I suppose, but thats tied to Void Century stuff with the WG so in reality its not him alone
4. Mihawk here, the problem is he's not trying to be "mysterious". Hes blatantly bored and wants to be left alone. Theres not motivation for him sans waiting for his duel with Zoro. Its a good and bad thing. It keeps it simple but I dont expect much from him outside of power.
5. Dragon doesnt necessarily have my interest anymore. Now we know why he started the RA but Oda refuses to give him and Garpna relationship which is weird as hell. At this rate, Garp will die before they even talk lol