That Nutkin

[Calysto]

The new limited job could be that shapeshifter.
FFXI had a system called Monstrosity that was basically that.

Edit:
But Could it really be related to the limited job that arrives late in the expansion ? teasing in in the release trailer seems strange then

[Yuella]

There's a nutkin enemy in FF5 that's really tough and can one-shot you.

[Chasingstars]

If this is actually yoshi-p giving a cheeky hint to green mage, and not just a gag, I think it would be interesting. As maybe its just me and my friends, but when you hear a job could perform "green magic" it gives off the impression of magic involving animals and plants.

[reginleif-]

To add to the theory of shapeshifting: there is a person disguised as a nutkin in a side quest in Sharlayan.

The image below is from the quest “Secret in the Box.” Please look only if you have completed it or are fine with spoilers.
The nutkin shapeshifter

If you haven't done the quest: it appears in Old Sharlayan, (x:10.6, y:11.1), after completing a lvl.*88 Endwalker main scenario quest “Outside Help.”