I don’t want to get into a drawn out discussion about this but I think there is a difference between choosing to sell at less than carrying value and market conditions dictating that you have to sell at less than carrying value, in which case the asset is impaired.
In my example the NRV would be more than cost, so the inventory is carried on the balance sheet at cost as dictated by IAS 2 but the business takes a decision to sell at less than cost in order to take on what it sees as a more profitable product. The product is not obsolete or damaged so can be sold for more than cost but a business decision is taken to sell at less than cost. Although not the same the concept of loss leading in retail runs along these lines ie one product is sold at a loss to attract customers in the hope that they will buy more profitable products. If the strategy fails you may record a gross loss but the ‘loss leader’ product is not impaired because you have chosen to sell at less than cost.
The key here is are you chosing to sell at less than cost or is the market dictating that you have to. In your example of housebuider in a market crash the inventory is rightly impaired, the NRV will be less than what it cost to build the house, it is not the builders choice to sell at this price.