I am able to go 10+ hours between bathroom trips. I'm not a pilot but I wanted to let you know that you will probably be able to do an entire flight without having to take a break. With your j-pouch you'll learn what works best for you. There are medications and supplements that you can take to help (Lomotil is prescription so I don't know how it would show up on a drug test.)
If you decide on the j-pouch you could put off the final surgery for quite a while and live with an ileostomy. That would give you a tremendous amount of bathroom freedom.
I definitely don't think getting a j-pouch would be a mistake for you and/or your career. Ask your surgical consultant for the names of those other pilots so you can talk with them.
kathy