I used CascView to extract the assets. Just point it at the HeroesData directory.
You can then make a SC2mod (saved as SC2Components to be able to copy files directly into it) and move the Heroes files into it.
I put thogether a working Heroes mod, but it's buggy as hell. For example: when placed on a map, units have their models duplicated and clipping through each other :S
If anyone managed to make a fully working Heroes mod, it would be cool if you could upload it somewhere with the assets removed (no point in including 8GB of models and textures if we can extract and put them back in ourselves).