I think we can final this.

This doesn't return so it probably doesn't get the string back to the user.

Instead of using getExceptionTitle(), it's probably cleaner to just call parent::__construct():

public function __construct($role) {
  parent::__construct(pht('Search cluster has no hosts for role "%s".', $role));
}

Then the exception will (string) cast normally, do something sensible for getMessage(), etc.

Having a separate method might be helpful if we expected to generate this exception in one language and wanted to be able to render it in a different language, but I don't think that'll ever happen with something low-level like this.