Once upon a time Smart Data Center (SDC) was still closed source. Back then it made a lot of sense to segregate open source SmartOS functionality from closed source SDC functionality. The differences between the two can be seen in the differences between the sample SmartOS build configuration and the sample SDC platform build configuration and the git repositories they reference.
Now that SDC is open source, the main reason for having separate builds (protecting proprietary source code) has disappeared.
Some of the benefits of platform consolidation
There is a bootparam passed in by grub on SmartOS media (“smartos=true”) that is not passed in to SDC nodes. The simple solution is to make the SDC platform image behave like SmartOS when it sees that bootparam.