I didn't read the article but I am familar with McDowell's views on this area, with which I largely concur.
Having previously supported the "below cost selling" ban imposed by the Groceries Order, I think there is now a clear case for its abolition. One only has to look at the preponderance of price competition in retail stores in Northern Ireland (and the relative lack thereof here) to notice the difference.
The fact that it is already legal to sell perishable groceries below cost in the South already makes the ban relatively pointless. Consumers are not stupid. In general, they notice higher prices and in general are careful not to be ripped off or fooled by "loss leaders"
Also, the knowledge that retail prices for non-food grocery items are prohibited by law from deflating below a certain level must provide a lovely cushion for distributors and maufacturers of such products. In the North, retailers are heavily slashing prices on goods like nappies and babyfoods. I would imagine they can only do so by negotiating discounts with their suppliers. In the South, this can only be done to a very limited extent so the suppliers enjoy ridiculously fat margins, at the expense of the consumer.