Currently the Teiid Connection Importer does not allow user to proceed with a MongoDB source. In Teiid 8.7, some capability to generate Mongo schema has been added (see linked JIRA).
We should allow user to select the MongoDB source. In general (for any source), if the importer fails to retrieve the DDL (or there is nothing generated) we should consider allowing the user to proceed. Just generate an empty model with the CP set on it. Then the user will have to manually model after import.