We currently use Cloudformation to deploy our Cloudfront distributions that sit in front of S3. Bundling our lambda@edge functions into a serverless app that includes the Cloudfront distribution would allow us to test & promote our CDN the same way we develop our applications. I would say that is a very valid use case and something relatively simple to implement once Cloudformation supports lambda function associations.
Of course, one could write a plugin that uses the API/SDK for Create/UpdateDistribution to shoehorn the event association in there instead.