Support for specifying "Volumes " (an attribute of an ECS task definition) would be very useful.

The application of this that I can see would be to map an EFS filesystem onto the instance and share it into the container as a volume so you can do persistent data storage (eg like this)

The application I had in mind, although I'm sure there's others, was to use it as a cache for package installs using composer to avoid downloading everything for every build (I imagine this would be a benefit for other package managers such as npm,  maven)