They may be grasping at straws, here. I mean, please... a dragon? This aint Spyro. Finding little random shapes in the "fire" on the concept art does not point to a dragon. I like the Navi theory though. The possibility of that hour-glass shaped woman with Link has the same oppurtunity of being Navi as it does being the Mastersword.
But the Link transformations are exceedingly popular. It's hard to think of a Zelda without thinking of the many shapes and sizes Link has gone through in the past many games. Deku scrub, wolf, little jawa creature, big blue fluffy flying bear thing, goron, zora, Giant, minish, DRAGON, a fierce diety, rabbit, child, adult, and probably many more I've forgotten. I confess, I have enjoyed all these transformations and would like to see more later on.
I like the Navi theory though. The possibility of that hour-glass shaped woman with Link has the same oppurtunity of being Navi as it does being the Mastersword. I have also noticed that the clothes of Link are based more upon the simplicity of the original OoT Link than the later TP Link, which could also point to the fact that it is the same Link as in OoT and MM. It might even further prove itself by not showing Link with the Mastersword, since OoT/MM Link had lost the ability to pull it from the stone. Then again, this is just speculation, and it's probably stupid of me to try and pull out theories when all we have is one small piece of concept art.