It makes sense. Not being able to render a template doesn’t mean that the requested resource wasn’t found, but that the requested format wasn’t supported. I think this is likely to be a developer facing issue - consumers of your routes will be consuming the formats you support, if you get this error then it’s likely while developing and either misnaming your template or not having added it yet.
Rails makes it easy to respond with a 406 if you prefer. Add a rescue_from clause in your application controller that responds with a :not_acceptable status.
Agreed with Matt’s response. I think it’s better for the developer to handle this situation with the response that they fell is appropriate instead of the framework telling you. Having this raise (and thus return a 500) is probably a better callout that something unexpected happened.