A) Using your settings I was able to create an order from the storefront that included items from different locations.

Result:
There were 2 items available at the Portland location, but only 1 of the ‘Portland’ line item sales got assigned a location.
There was also an item that was not available at the Portland location, and it did not get assigned a location.

Example:
SKU: 210000000764 - Assigned to Portland
SKU: 210000000475 - Not assigned to any location, but available at New York
SKU: 210000000325 - Not assigned to any location, but available at Portland

See order:
https://multilocation.kosmoscentral.com/wp-admin/post.php?post=1599&action=edit

Note: If items are not assigned to a location then merchants would need to use an order status that does not get applied automatically to WooCommerce orders (and is not used for other purposes) to trigger the sync process so they can manually assign locations to each item before syncing line item sales.

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In addition to the current settings I enabled settings for:

B) Automatic order routing

Result:
When I attempt to add items to my shopping cart that are not available at the Portland location the items are removed from the cart and an error message is displayed.

Question:
For split orders Is it possible to assign each line item to a location automatically once a WooCommerce order gets created?

Note: This would be ideal for the integration since it would allow split orders to get synced automatically once an order is placed online.

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C) Show assigned warehouses at checkout

Result:
I was able to create an order that included items from different locations. All line item sales that were available at the Portland location got assigned a location, and any line item sales that were not available at the Portland location did not get assigned a location.

Example:
SKU: 210000000764 - Assigned to Portland
SKU: 210000000475 - Not assigned to any location, but available at New York
SKU: 210000000325 - Assigned to Portland

See order:
https://multilocation.kosmoscentral.com/wp-admin/post.php?post=1607&action=edit

Note: As long as all the line item sales for 1 location are automatically assigned to a location the current integration could automatically sync the line item sales from WooCommerce for the 1 location once the order was placed online. For items that were not automatically assigned to a location the merchant would need to apply a different location (that does not match the location assigned to the initial set of line items), and the sync process would export the rest of the line item sales once a location had been assigned.