So, I came across an interesting theory. Want to know if anyone else has heard this before.
Basically, Luffy's four strongest fighters (Zoro, Sanji, Jinbe, and Carrot) will be known in the future as the Four Dignities. The Four Dignities - from my understanding - are four ancient Buddhist symbols that represent the aspects of Lungta. Oda has used Buddhist symbolism before, (Asura and Sengoku's devil fruit power) so this isn't too far fetched in my mind.
The four dignities are the tiger, snow lion, garuda, and the dragon, and each of the 4 crewmembers/allies of luffy I listed above correlate with one of the dignities.
Tiger (wind element) - Zoro (he has been associated with this animal in color spreads and figures)
Snow Lion (earth element) - Carrot (she is a snow bunny and su long means moon lion)
Garuda (fire element) - Sanji. His father's epithet is "Garuda" and Sanji utilizes fire when fighting of course.
Dragon (water element) - Jinbe (eastern dragons are traditionally aquatic)
Of course, this theory only works under the assumption that Carrot even joins the crew.