Without either of these changes, you can already Filter the Physical Inventory by "To Apply" and export the product, on hand quantity, value, counted quantity, and difference to calculate the variance outside of Odoo.

To do this inside Odoo, one of the following solutions should work:

UPDATED FOR Odoo 19.0:

Create a custom x_variance field:

Use an Automation Rule (this will NOT trigger Line of Code - LOC - maintenance charges):

record.value / record.quantity * record.inventory_diff_quantity if record.inventory_quantity != 0 else 0

Then finally a Custom View like this:

<data>
    
<field name="quantity" position="after">
  <field name="currency_id" column_invisible="1"/>
  <field name="value" groups="account.group_account_user" 
         sum="Total" options="{'currency_field': 'currency_id'}"/>  
</field>

<field name="lot_properties" position="after">
  <field name="x_variance" groups="account.group_account_user" 
         sum="Total" options="{'currency_field': 'currency_id'}"/>    
</field>

</data>

This restricts the value and variance fields to those in the Accounting --> Book Keeping group.

Result:

UPDATED FOR Odoo 18.0:

Given the following values and costing methods for Products:

The Physical Inventory Menu would then show something like this:

Here, the loss of 1 unit of each product has a financial impact of $29 in lost value.

Custom Field (this WILL trigger Line of Code - LOC - maintenance charges):

Dependencies:

inventory_quantity_set, product_id

Compute:

for record in self:
    cost = 0.0
    if record.inventory_quantity_set:
        product = record.product_id
        if product.cost_method in ['standard', 'average']:
            cost = product.standard_price
        elif product.cost_method == 'fifo':
            valuation_layers = record.env['stock.valuation.layer'].search([
                ('product_id', '=', product.id),('remaining_qty', '>', 0)], order='create_date asc')
            qty_to_consume = abs(record.inventory_diff_quantity)
            cost = 0.0
            for layer in valuation_layers:
                if qty_to_consume <= 0:
                    break
                qty_from_layer = min(layer.remaining_qty, qty_to_consume)
                cost += qty_from_layer * (layer.unit_cost or 0.0)
                qty_to_consume -= qty_from_layer
    record['x_impact'] = record.inventory_diff_quantity * cost

Note: these are prototypes, not solutions, and make assumptions about how products are deplenished from inventory (financial fifo). Your Odoo Digital Advisor or Odoo Partner can help you implement something similar in your own Odoo database. You can also extend these approaches to calculate the percentage variance.