User namespaces will come. Patches are in progress and you can refer to github for the status of that effort.
I'd hesitate before calling it a "security problem" with Docker. It's a highly-requested security feature. The absence of it makes containers less secure, but does not make them vulnerable. There are use-cases for Docker without user namespaces, but user namespaces will make Docker better and will make containers more secure.
We do distinguish between the security of the Docker engine and the pieces of our ecosystem and the security of containers themselves. We seek to improve both.
Vulnerabilities such as the one fixed today in boot2docker 1.3 whereby either web browsers or containers may control the Docker daemon and perform remote code execution are serious issues in Docker itself and/or its ecosystem of products. Resolving such vulnerabilities is not, for me, less important than adding user namespaces.
