Steem-Engine is working on the regulatory requirements to be able to allow people to purchase steem directly. While this doesn't appeal to the largest audience of traders, it does solve most of your problem as being an on-chain avenue for people to directly buy Steem and only requires a few steps to power up.

I would love to see Coinbase become part of its Earn program. With all the new upgrades that have come to Steem recently and are about to be adopted, would be a good way to get that news out and allow people on Coinbase to trade Steem.