Presently the only available use for context/project level env configs is within command line arguments and bash scripts. However, there are areas where environment vars would be useful being interpolated into other configuration sections of the yaml file. Such as declaring environment configuration for requested images in the initial docker block of the config file. It would be great to be able to take advantage of contexts beyond just bash scripts and command blocks.
Currently in order to configure services in a custom manner you must use a series of docker run commands. This also forces you to run any tests/integration steps inside an additional container to talk to those services (for us this adds 30s - 1m of building a new docker image and spinning it up which contains the new code on each commit which should be an unnecessary step).