Very nice Jim Simon!
In addition to allowing searchable_fields to be explicitly defined on the Django model you might also include indexing all fields on a model by default. You can get the fields of a model and their internal type with:
fields = model._meta.fields
for field in fields:
You’d need a function that translates the fields internal type to ES types. This could be done with an if statement in a separate function. That way you’d achieve a smarter solution that automatically maps each field with correct type.