Why it requires Commerce Order?

It really doesn't. The initial thought was to use it to replace some of the order based displays during checkout.
I can work up a patch that would remove the dependency for the commerce_order table as a base and allow any arguments and only pass the order id to the view if the first argument is order id.

Thanks for the patch! I took the same idea in your patch a little bit further.
The attached "...-3.patch" has 2 new functions for:

• Get the position of all order id arguments
• Build the arguments array based on the order id positions

Then the checkout pane uses the build arguments function for the array that it passes to the views execute function.
The patch also includes the updated README instructions.

I've tested this with a node view as a checkout pane, and it rendered correctly.
Test it out and then I can get it committed.

I like the direction as it would make it more flexible instead of always sending order_id in those argument positions.

Some items that need updated / consideration:

• The settings variable name in your patch made me realize that the pane id should be prepended with "commerce_views_pane", ie module file, line 65 should be
  

  $panes['commerce_views_pane-' . $result['pane_id']] = $result + $defaults;
  

  Then all the splitting would need updated to account for it. This would make the pane and settings variables unique this module.

• The key of the arguments array returned by $view->get_items('argument', $display_id) is the views argument id, not the field name, which is why I had a check for $arg_data['field'] == 'order_id'. The arg id could be order_id, order_id_1, etc if there are more than one. So in the settings form, it would check if the 'field' was order_id to provide the suggested default.
• _commerce_views_pane_view_build_order_arguments()
  • For the arguments array to match what views would be expecting, it should always add a NULL to $return if !isset($arg_data['field']) AND nothing is being added by the settings. There could be an argument that doesn't have a field, perhaps view global null or something.

I'll open up a separate issue for the pane id changes. For this patch, we can focus on making the settings variable building and splitting account for it.

pane id creating and parsing fixed per #1952772: Pane id should be unique to this module. The patch in this issue will need to use the helper functions for the pane id creating and parsing.

The variable name with underscore would be ok since we're never splitting it apart to extract the view id or display id which are allowed to have underscores, hence why the pane id is "-".

Thanks, I've committed per http://drupalcode.org/project/commerce_views_pane.git/commit/9afb65a

nice catch, I updated it to match the README

It's not clear to me how to set the Order ID argument now. I actually liked the module more before this change!

So, since Arguments = Contextual Filters in Drupal 7 Views UI... How can I set the Order ID Contextual Filter? Does it only offer it on views where the content relates to orders?

Thanks for the help!