Overreaction? Let's hypothetically consider yaml+, with the definition:

  yaml+ = yaml "\n" "."

* easy to wrap a yaml parser and create a yaml+ validating parser.

* easy to create a simple script to validate the end-of-file dot line.

* easy to create a presubmit check to validate yaml+

* easy for an editor to syntax check the end-of-file dot line.

Assuming there are other redeeming qualities of YAML, the truncated YAML problem can be solved with minimal effort.