We've finally rebuilt steal. It's going to be amazing. It supports ES6, CommonJS, AMD and steal's legacy syntax. It is able to do the multi-build and pluginify. It also doesn't evaluate your code while building so its less error prone!
It's still a ways from production; however, it is able to build:
And, I used it on DocumentJS's CanJS app.
Steal is now split in two. There's the client StealJS, and the build tools StealTools.
I've started to put instructions on how to use the client and build tools: