The last month, Bittrex is busy maintaining the NEO wallet. This is to the great displeasure of many users of the exchange. It is not possible to get your tokens directly from the exchange, so the tokens are fixed.
Malcolm Lerider
Malcolm Lerider from NEO research and development has come out so it is rumored that Bittrex is working on an update to ensure that new trading pairs become possible. Think of BTC / GAS and all (future) NEP5 NEO tokens. With emerging exchanges such as Binance and Kucoin, Bittrex is forced to catch up, otherwise more and more investors / day traders will use an alternative.
Bittrex has not yet made an official statement. How long this will take is still the question.