thinking about possible API for this.

My first thought was to add a Options property in template map that lets user enable the auto inclusion of system parameter resources:

{#eid :StackName 
 {:Options      {:SystemParameters true}
  :Resources  {:MyResource [:Service.Module {}]} }}

But I dislike that I'm mixing infra properties into a map that should consistent of only AWS Cloudformation options.

So a better alternative may be to stick with reader literals for config manipulation. We can add a #with-params literal that does serves same purpose as above option:

{#eid :StackName 
 #with-params {:MyResource [:Service.Module {}]} }

With this alternative, I dislike that this reader literal is only meant to be used in a single context (when declaring resource options). But I guess that's OK since the scope of this reader is for AWS templates.

Another concern, that might make this more cumbersome, is that resources are mapped based on their logical identifiers (local to stack) not their physical identifiers (global to user's aws account). But perhaps I can just use AWS's ref templating utility so that identifier strings can be replaced by AWS at creation time.