Fuegoleon is most likely going to be the next Magic Emperor,he has the Skills and Judgement for the Position,he woke up from his Coma,and he got the Salamander PowerUp at the same time which leads me to believe so. Having a Spirit to aid your Magic Capabilities is a very handy thing to have,just watching Yuno proves as much.
Yami would/could be a Candidate for Magic Emperor as well in my Opinion,but he strikes me as a rather laid back Guy and probably wouldn't want the responsebility. He'll remain Captain of the Black Bulls.
Speaking of the Black Bulls,i noticed that we don't know who their Vice Captain is,i believe it is either going to be Zora or a new Member/Character joins the Black Bulls taking the Position. I doubt Asta will be the Vice Captain to be honest,he will keep the Underdog Role in his Rivalry with Yuno and watch him become Vice Captain first to get motivated to rise above as well.
Nozel isn't written down as a Candidate for Magic Emperor for me unless he actually does something impressive and worthy of succeeding Julius soon,i guess within the confines of the Story it would be logical to have him as a Candidate though. No Questions asked,he still is a Captain with Skill and Intellect and is very committed to his Duties as such. One of my favorites even if he hasn't done as much as Yami for example.
Meleolona will remain Captain of the Crimson Lion,if Fuegoleon does end up as Magic Emperor it would mean she remains relevant to the Story and can continue to provide some Comedy and Badassery for us. And also because Leo is hardly able to take over a Squad just yet,i wouldn't mind him becoming her Vice Captain though.
The Golden Dawn needs a new Captain,i believe we may get introduced to a new Character when it comes to it.
Yuno is talented and quite Powerful,since he joined the Magic Knights he has managed to impress Julius and all the Captains as well not to mention even the Undercover Licht (William!) when he was his Captain. But he may lack the Experience for the Job,so for him i can see the Vice Captain Position as fitting too.
Those would be my thoughts/guesses on what is going to happen next.