How to Add a Campaign Skip

Instead of choosing your Class in the loading screen, enter the game as an unclassed "Exile" and fight through the first zone.

After killing the Miller, enter town, and be faced with a choice, of which Way to follow, which Class.

In the endgame, for an appropriate cost, whether its 1,000,000 Gold or a currency Orb that drops from the Arbiter, a character can forsake the Way of their original Class, become an unclassed Exile again momentarily, making availability to choose another base Class on the same character.

As long as you need to finish the campaign with at least 1 char, I would also be opened to a campaign skip for subsequential characters.

I'm not sure on how exactly it should be implemented.

But all the quests that were previously completed by a character that completed campaign, should be able to be 'cloned' on the new char you are making.