Quoted from PinLen83:
This would require a recalculation of scoring for "Stay Puft". Everyone would choose that mode as their first due to the insane amount of points it awards. Giving you the option, and Maybe not allowing the final mode in each ladder to be a choice is a great option.
This is a great idea. The final mode would always be last, but being able to choose the order of the others would definitely freshen things up.