sale_order_line_sequence/view/sale_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>

        <record id="view_order_form" model="ir.ui.view">
            <field name="name">sale.order.form</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_form" />
            <field name="arch" type="xml">
                <xpath expr="//field[@name='order_line']" position="before">
                    <field name="max_line_sequence" invisible="1"/>
                </xpath>
                <xpath expr="//field[@name='order_line']" position="attributes">
                    <attribute name="context">{'default_sequence': max_line_sequence}</attribute>
                </xpath>
                <xpath expr="//field[@name='order_line']/tree/field[@name='product_id']" position="before">
                    <field name="sequence2" string="Secuencia"/>
                </xpath>
            </field>
        </record>

    </data>
</openerp>