It's the end of budget airlines as we know them

• Southwest Airlines is ending its famous open-seating policy.
• Assigned seating could generate up to $2 billion in revenue for Southwest, one analyst estimated.
• The change represents a larger evolution of budget airlines' business models in the US.

Budget airlines are upending many of their original business plans as increased costs wreak havoc on their bottom lines.

On Thursday, Southwest Airlines announced the end of its open-seating policy, a 50-year practice of letting passengers choose their seats based on their boarding order versus having them assigned.