Resource Groups are one of coolest but most obscure features in AWS. My theory around that was around due to the powerful search bar in EC2 AWS Management Console which can accept regex, range queries and auto-suggest the tags and their values. This is looks good as long as the components you manage are only EC2 instances.
CloudFormation automatically creates a tag called aws:cloudformation:stack-id which gets applied to all of the entities created / managed by CloudFormation – AWS uses it internally to logically group the components created by the CloudFormation. The aws:cloudformation:stack-id is pretty much all that’s required to create a Resource Group.
I would like to request AWS to consider the feature like a button in the CloudFormation windows which says – Create a Resource Group which would take you the Resource Group windows to view and manage the entities at a single place.