Question: Is it possible to somehow unpack a bundle? I need to make sure all packages within a bundle are signed correctly...

TIA

Answer: 
Dark.exe decompiles bundles; use `-x` to extract the bits.
Run the installer with the argument `-layout` and it should download or extract (as appropriate) the packages that it contains to the directory the installer is in. You can specify a target directory as a second argument if you wish.

This was tested with a bundle created with version `3.6.2520.0`. It is known to be broken on the current weekly release of `wix36.exe` itself.