Well, we haven't got it all to work with Babel 6 yet ;) But, here's the two big things that have made this process slow:
- Decorators - Aurelia and it's developers make use of the ES 2016 proprosal for Decorators. When Babel 6 was released, they dropped support for this. That was a deal killer for us. Now, there is a plugin based on the same spec as Babel 5. That solves one of our problems.
- Plugins and Ecosystem - There are lots of things around Babel that need to be updated to work with the new version. For example, the pluggin Babel into Karma. Also, we had a plugin for generating TypeScript d.ts files from Babel. That needed a complete re-write. So, it's the forced upgrade of the entire ecosystem that has taken time. Those things are falling into place now...so we expect to be able to move everything to Babel 6 soon.