We seen them passionately kissing in "Bender's Game" (In the Cornwood universe, that may prove their bisexual "though it was kinda non-canon", which I found quite hot.) I think it's very unlikely they'll engage in romantic activities ever again (Since they both got boyfriends now.), unless it's an "Anthology of Interest" episode (Might like to see that.) or a non-canon episode like the "The Futurama Holiday Spectacular" (Might like to see that too). But I want to know what you think.
I would be a little annoyed if they did an episode where Leela and Amy would break up with their boyfriends, just for an excuse for a short brief lesbian relationship. Then have a fight, and then go back out with their boyfriends in the end of the episode.
However, Leela and Amy may kiss again in front of Kif and Fry just to "please them". However, I think that mightn't never happen.
Yet, there's always fan fiction, fan art, fan comics and "The Turanga Pages" for Leela and Amy.