I don't know if I would personally see the need for it as there are products like magneto, prestashop and woocommerce which do that already.
I think he is talking about implementing shopping carts like magneto, prestashop and woocommerce into peoples websites.
Shopping carts are complicated to setup and the average user would have a problem. You have the styling and layout to modify as well as all the categories, products, postage etc.
I think there could be an opening but I do not know if you would find enough custom to make it a business.