That is not what union budget says. It only says amenities in existing coaches will be upgraded to VB like standard. It is not feasible to convert existing LHB coaches to VB. They can probably add automatic doors and coach displays etc. like VB, only upgrade of internal amenities is feasible. Also no train will be replaced by VB. There will be a lot of new VB introduced. And maybe slowly, if non VB trains become unpopular, they will be withdrawn over time. But no immediate conversion.