Quick note for those interested!
The first removal of the year for BitTrex will take place on January 12th, 2018
The following markets will be delisted by then:
BTC-DGD
ETH-DGD
BTC-TRIG
BTC-MTL
ETH-MTL
Don't leave yours loose!
Source: https://support.bittrex.com/hc/en-us/articles/115003816652-Pending-Market-Removals-1-12-2018
They never give reasons why they delist coins.