With 9.0.1 I can create a new theme that extends the OneUI IDX V1.3 theme by adding extends="oneui_idx_v1.3" in the start tag like so:
<theme extends="oneui_idx_v1.3"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="platform:/plugin/com.ibm.designer.domino.stylekits/schema/stylekit.xsd">
<resources>
... *resources* ...
</resources>
</theme>
What do I specify for the extends attribute to extend the Mobile default theme?