I'm guessing Sony figures the Slim can directly compete with Xbox One S regardless of the 4K features because of the performance gap that still exists.
Sales in NA are virtually like for like with XBox One and PS4 at the moment due to the new S model. And remember that the PS4 is currently $50 more expensive than the One. I would be extremely surprised if Sony don't reduce the RRP of the PS4 to $299 at the most frm the current $349 price. Although considering the price saving and reductions in build quality and features, I don't think its beyond Sony to bring it further down. So fully expect it to be between $249-$299.