We'd like the ability to track our sales by location, very similar to how you can already track the inventory by location. In other systems we've used, we've seen this called Sales Channels. For example, we sell at retail online (Magento) and also at wholesale thru a dealer network. If we could have a field that allowed the sales to be set to a particular sales channel and mapped to Xero as a tracking Category, we could run financial reports by sales channel to see how each channel was performing. Other uses of this could be businesses that have multiple locations where they sell products...for example a business could track sales at one store against another store.
For what it's worth, the linking of attributes to Xero categories is a killer feature; it's a huge advantage over competitors. Any attempt to make it better will further entrench Dear as the first choice for larger businesses.
This is not an answer, but I just wanted to clarify for other people reading this that mapping location on the sale order to a Xero tracking category does more than mapping inventory; it maps sales as well. In other words, I think you are requesting for a sales channel to work like location does.
Could you not use the Sale Rep field? It can be mapped to tracking categories I think.