Add the ability to provide an origin address to ITaxProvider interface GetTaxRate method

I am working on a tax plugin for our 3rd party tax provider, and need to provide both origin and destination addresses to their tax engine for determining tax in states with origin-based taxes (Illinois, etc).  We have 13 warehouses that our products ship from, so the origin address can vary on each order line (3.50 release is great for this!)

I was thinking if CalculateTaxRequest was extended to have the following, it would allow the flexibility needed:

public class CalculateTaxRequest
    {
        public CalculateTaxRequest();

        public Address DestinationAddress { get; set; }
        public Address OriginAddress {get; set; }
        public Customer Customer { get; set; }
        public int TaxCategoryId { get; set; }
    }

Just a thought, thanks for a great product!