"XMI is a way to save UML models in XML"
Therefore, XMI can be a way to save the class-and-association structure of Simile models in XML.
Therefore, XMI can be leveraged (along with MathML, GraphML, Dublin Core...) to provide a standards-rich language for Simile models, and save a lot of work in the process.
Perdita Stevens: MOF and XMI - a mini-tutorial. http://homepages.inf.ed.ac.uk/perdita/XMI/tutslides2up.pdf