It would be nice to have a support for dumb merging YAML files:

YAML files can consist of multiple parts separated by --- so what we need is just a AppendingTransformer which would append new line and ---

see https://github.com/johnrengelman/shadow/blob/master/src/main/groovy/com/github/jengelman/gradle/plugins/shadow/transformers/AppendingTransformer.groovy#L53