Now, I recall that some accounting usage want to separate the expense/revenue for the same product depending on the destination. For example, one account for purchase/sale in the country, one for CE and another for out of EU. Usually it is for tax reporting but this is managed by the tax line in Tryton.
We could have an extension of the tax rule to replace the expense/revenue accounts but it seems over engineering to match an old manual usage. Also in case of mistakes it is much more complex to fix a posted move in the wrong account than a tax line.