purchase.Line missing TaxableMixin

We wanted to have our sales quotations and purchase orders be like invoices, with the taxes on the line being an index into the taxes table... so for sales this was more or less straight forward to do, but when working on purchases we noticed that TaxableMixin was missing on the Line() class definition.

For a proof of concept we made a simple module to add TaxableMixin as well as the functions taxable_lines() and _get_tax_context() to purchase.Line.

Seems to work okay, so the question imposes: is there any reason not to add TaxableMixin to the base module purchase.Line?