Cloned from launchpad blueprint https://blueprints.launchpad.net/heat/+spec/output-default-params.

Description:

Say you create a stack with some stuff to be shared by other stacks. SecurityGroups, Networks, etc. If you have a lot of these shared resources in the stack, you must lookup, then pass a lot of parameters to a second stack manually.
The second needs a feature that lets you pass the name of the first stack, and then it can set parameter defaults to be the outputs in the first stack. You can then override individual parameters still if you want.

In the default param of the second stack, Perhaps there could be something like:
"Parameters": {
    "BackendNetwork": {
        "Default": {"StackOutput": [ "StackA", "NetworkId"]},
        "Description": "Network to use",
        "Type": "String"
}}


Ideally, the stack name would support ref's as well, so 
{ "StackOutput": [ {"Ref": "StackAName"}, "Foo"]}

This way, you can specify which instance of the stack to pull values from.

Specification URL (additional information):

None