Hi Marcian,
As per the pluggable widgets documentation by Mendix, the datasource type has to be of type list:
https://docs.mendix.com/apidocs-mxsdk/apidocs/pluggable-widgets-property-types#datasource
Also, if you change the type of object, it would require a change in the logic already built within the widget to ensure that it works as expected. Though, looking at the doc it does not seem possible for pluggable widgets.
If its a widget based on Dojo, then I’m not sure.
Hope this helps!