Why not? After the dragons gathered, they went back to the priest and the priest told him that the sword and shield needed more time before they'll appear. Which meant that they are definitely not Hak or SooWon. Shortly after, Taejun and Lili were introduced. So isn't it referring to them?
Also, there have been many instances in the recent arcs that Lili and Taejun fought and protected Yona. Isn't that what the sword and shield are supposed to do? After all, just the dragons aren't enough to bring Yona the throne. Should there be war, she will need an army. Lili holds the power of the water tribe army and Taejun holds half (or maybe more) of the fire tribe army.
We know that Zeno was the dragon born to be the shield, but who is the sword?? Is it Kija??