Payment Account Number is missing, this is used to make sure the returned rates are specific to your DHL account.
IsDutiable would be a great feature, depends how much work you think it'll be as im not sure what else you would need to add, i think total cost, maybe more?
There's also another carrier option for us when sending from UK to France and other EU countries.
<LocalProductName>ECONOMY SELECT EU</LocalProductName>
<ProductDesc>ECONOMY SELECT EU</ProductDesc>