What fault of open source is it? Its very nature? Amazing that we have many vendors who do cooperate with us then.
A stable binary API has been discussed to death. It creates more work for kernel developers to maintain it, and by definition is lower performance than writing a native driver. There are people working on such a thing regardless of its potential shortcomings, but don't expect to see it in the mainline kernel unless it doesn't place an undue burden on mainline development.