A Southwest commercial airliner takes off from Las Vegas on Feb. 8, 2024.Mike Blake | ReutersSouthwest Airlines is ending open seating and will offer extra legroom seats on its airplanes as mounting pressure on the carrier to increase revenue prompts the biggest changes to its business model in its 53 years of flying.The airline plans to start selling the first flights that will offer extra legroom next year, it said Thursday. It also plans to begin overnight flights, starting in February.Southw...