What would you like to see?

Many files having unknown extensions can be correctly processed as text files; I'd like to add a configuration option which would change the default behavior when a file's type is unrecognized from "display an error message" to "treat as text". (Longer-term, it would be handy if a file's type could be specified/overridden when it was imported, but that would take a lot more effort.)
Conceptually related to issue #2638