Welp, believe this or not, I've read where serious riders shouldn't 'do' ballet. Something about the muscles and movements counteract each other. It's been a good 5-6 years since I heard of this. I asked on another horse board if anyone had heard of this and surprisingly, quite a few had.
Michael Poulin and his crew took ballet. I heard him tell the story in a clinic. He said it greatly improved their proprioception, coordination, balance, etc. He did mention that they told the instructor beforehand that they needed to do everything flat-footed and without turning toes out, but he said it was incredibly helpful.
He can still do some moves, even wearing riding boots in an arena.
In order to think outside the box, one must first know what is in the box.
I do Crossfit and if that doesn't mess with riding then NOTHING will! As a side note: I'm schooling 4th/PSG dressage on a very difficult to ride horse and the owner thinks it's beneficial that I am doing Crossfit and am very strong otherwise. I don't get tired at all riding and I feel like I have better control over my body since Crossfit. Now, there are some days when my muscles are really sore and that makes riding a little more of a challenge...
When I took a short break from riding a picked up ballet as my activity. Granted, it was only once a week and only lasted for a couple of months (I couldn't stay away from horses for too long ), but it did help my riding some. I got more flexible and limber and it really helped me when my instructor had me do exercises to help my seat and leg.
If i smell like peppermint, I gave my horse treats.
If I smell like shampoo, I gave my horse a bath.
If I smell like manure, I tripped.
I've just started ballet class 2x week and love it! I even got a leotard, tights, and little skirt to cover my butt....
So far I love it. I'm middle-aged, I guess, so no chance of me becoming a professional ballerina; my body is fully developed so there's only so much turnout I'm going to get. I don't have flexibility in my ankles (heels down has always been an issue) so have a hard time with grand plie in second position.
The workout is great and it inspires me to try to be more graceful, which I think would somehow help me in the saddle (but I'm not sure how yet).
I don't know, I think that if you like it and it is fun and interests you then you should do it!