Not only would this voucher have to be expensive you guys seem to be forgetting the technical part of the issue. They would have to add another system to the game which can automatically re-seal all of your items so when you change to another class you also get the relevant weapon and accessories, soul badge, mystic badge etc.
Just changing the class wouldn´t fly considering the playerbase, they would want their items intact too for the new class. So I see a huge headache for NC that they dont want. They screwed up with the White Orb fiasco, so I really doubt they could make something as a class change voucher.
IMO