Many argue that towards the end of the series, Luffy will fight against Akainu. Both are leaders and both use fire kind powers plus Luffy will want to take revenge for Ace.
Zoro will fight against Fujitora (both are swordsmen and honorable fighters) and Sanji will fight against Kizaru (speed based fight and both are related to science).
This leaves Aramaki out. Now, since Jinbe has officially joined the crew it makes sense for him to fight against Admiral Green Bull.
1- First, we have to consider Aramaki’s character theme of oppression. I think Jinbe is the perfect Straw Hat to prove him that his view is wrong because of the fish folks past with oppression.
2- Aramaki states in Chapter 1054 “My logia is nature incarnate! A source of life that rivals the seas!” (Scans)/ “The forrest is just as much the cradle of life as the sea!” (Official translation). This could be a foreshadowing for a fight with the First Son of the Sea.
3-Could be an interesting fight given the fact that Aramaki can absorb liquid while Jinbe fights partially with water. So either Aramaki takes Jinbe the possibility to fight with water or maybe he uses more water than Aramaki can absorb.