Didn't see the actual repo linked: https://github.com/joyent/sdc-docker "A Docker Engine for SmartDataCenter, where the whole DC is exposed as a single docker host. The Docker remote API is served from a 'docker' core SDC zone (built from this repo). ... Disclaimer: This is still very much alpha. Use at your own risk!"
To me it seems like Triton is about shoehorning Linux into Solaris/SmartOS containers. While this seems great for accelerating adoption, why not just use SmartOS-specific Dockerfiles/repos in conjunction with sdc-docker (Not directly addressing the parent, more of a general question)? Imagine all of the crazy bugs and edge cases that will arise when trying to run Linux binaries on UNIX. I'm surely making some assumpt…
There are also different philosophies about whether container images should be distributed as source (Dockerfiles) or as binaries. It looks like Joyent decided to run Linux/x86-64 binaries to be on the safe side.