This is not supported yet. However, this is quite easy to build. Please file a feature request in the Support Portal if you need this.
XMI is an important standard to exchange UML models between applications/tools, so more or less same question as previous ones?
When will Mendix Studio Pro support import of XMI (XML Metadata Interchange) formatted model content? It would be great to have such feature allowing users to jump on the Mendix train.