bittrex assess all coins with this:

Thanks for the request. Our policy is to not comment on whether we will launch coins but we mainly add coins due to community demand.

We gauge demand based off of tweets, hash power, length of bitcointalk thread, volume on other exchanges, etc. Follow us on twitter @bittrexexchange and tweet about how much you like this coin and Bittrex. We respond to creative and insightful posts to help market your favorite coins and Bittrex. I'd also consider coming to our irc channel #bittrex on irc.freenode.net and do some guerrilla marketing. The traders there can help you gain exposure for your coin.

Thanks,
Ryan @ Bittrex