RC0 - where is build file?

In the very distant past Ionic 2 used webpack for build process, then they moved to gulp. I believe they moved back to webpack with RC0 but currently starter project does not seem to include any build file. I guess they moved it to CLI project. It is rather problematic because my app had a custom build pipeline implemented that did some custom TS file compilation related to web workers. Because web workers are started by referring to .js files and because of that worker files need to be separate from the main app bundle. How is the build process handled now and whats the recommended way of customizing build pipeline? Use case here is a need to compile some separate TS files that need to end up in separate JS files.