Thanks for reaching out.  We spent a lot of time, energy, and money to add NXT to Bittrex.  Unfortunately, we delisted it a few months later because there was no demand for it.  

Truthfully, the whole experience left a bad taste in our mouths so we are weary of NXT clones.  Bringing an NXT like coin back means more support headaches and burden so we'd only do it for the right coin.  I'd personally love to see an NXT clone on our exchange be successful because it would at least break us even for the cost of adding NXT.