Once a symbol of affluence, the stretch limo has largely fallen out of favor as the rise of Uber and Lyft, the Great Recession and new regulations hastened a shift to chauffeured vans and S.U.V.s.

Over a few days in early March, carmakers and limousine company operators gathered at the MGM Grand in Las Vegas for an annual convention, where they went to panels and parties and admired shiny new ...