It has either not been decided to add new assets for GDX or Coinbase. This wave has taken a step to eliminate the rumors that Bitcoins centralized competitor can be offered in the US for major trading platforms.
On this announcement, this wave lost market capitalization of some $ 30 billion. These exchanges said in a blog post that on the contrary, reject any statement.
Source - https://news.bitcoin.com/ripple-dips-after-coinbase-rejects-rumors-of-a-new-asset/