I can't possibly be the first person to come up with this... But I also can't find anything on Google. Under the Casting Elemental Spells section under Monk on page 80, it says to "See Chapter 10 for the general rules of Spellcasting" and keeps referring to using these abilities as "casting" and disciplines as "spells". Because of this, I'm inclined to think this really is "casting a spell", just using Ki points instead of spell slots. Page 67 specifically prevents spellcasting while in animal form, "You can't cast spells..." so this probably wouldn't work. I think this is worth a tweet to Crawford and Mearls for clarification though. Somebody wanna do the honors?
If it's okay, and you can cast these while in animal form, then what would be the best Elemental Disciplines?
Water Whip looks useful, not just for the damage, but for the 25ft pull as a tanking bear. What else?