Coinbase is exploring a range of new assets and "Steem" is one of them!.in the picture bellow you will see all the coins Coinbase is interested in,some of these coins will be added to Coinbase custedy acording to Coinbase.news from Aug/03/2018.
For much more detailed information on the subject.head over to The Coinbase Blog Link:https://blog.coinbase.com/coinbase-custody-is-exploring-a-range-of-new-assets-e700496844be 
Bitcoin donation address: 1LF43z7XgLC34mf9bLQTrv8utDydJBC6bn