A Khan on a Hakkapeliitta supporting a load of adjacent Caroleans is awesome. It's worth finishing the Patronage tree as Sweden for that alone, as you can usually get a Khan from City-States before you launch an attack. Note that the Khan bonus doesn't seem to stack with Medic promotions, but it might with the Fountain of Youth promotion.
As the Ottomans can steal naval UUs, they could potentially field a Turtle Ship/Ship of the Line force. Painful.
And on the subject of promotion paths...
Kris Swordman with +1 move and attack promotion -> Berserker. (and later -> Norwegian Ski Infantry for super-fast hills movement)
Persian Kris Swordsman with the +1 move and attack promotion. With Blitz, you can attack three times then move a tile - switch in another unit for safety.
Kris Swordsman with the +1 move and attack promotion -> Janissary.
Kris Swordsman with the +30% defence and +20 HP heal-per-turn promotion -> Carolean
Minuteman -> Norwegian Ski Infantry.
Incan Norwegian Ski Infantry. With Mt. Kilimanjaro.
Combat bonus in Forest/Jungle (33%) seems to be listed twice in the Civilopedia. I wonder if this means you can go Jaguar -> Mohawk Warrior for a 66% bonus? Even if that's not the case, Woodsman and the Iroquois UA probably stack well together.
Immortal -> Winged Hussar. Healing up becomes somewhat easier (you'll need the March promotion for maximum effect.)
Immortal -> Impi -> Rifleman. Now, you can take that double heal bonus into the infantry line! Shame Immortal -> Carolean is impossible. You'll have to just look for the Fountain of Youth for that.
Songhai Conquistador. You won't need to escort this unit in the seas, assuming the embarkment defence stacks.
Mongolian/Persian Comanche Riders. The maximum potential doesn't last long, but having 6 moves ain't bad.
Forest Elephant -> Keshik for both Great Generals I and II.
Zulu Keshik. Eat those promotions up!
Japanese Jaguar or Janissary. Bonus points for promoting a Jaguar to a Samurai.
This is fun!