I'm in the beta and can say that most of what they are implementing is not going to require that large parts of the game code be rewritten or lots of new art assets generated. It's mostly from a game design standpoint. In fact, pretty much all of the changes have already been implemented in the beta. Some of the highlights are below.
- Removed Scrolls of Identification, you now simply right click an item to identify it.
- The fifth quick slot button is now a dedicated potion button.
- The mystic artisan has been removed, reasoning is that it was too similar to gems/sockets.
- Selling and salvaging from out in the field has been removed.
- Blacksmiths now salvage items and white ones are no longer salvageable.
- Added a dedicated Town Portal button that does not require scrolls.
- Names of the main stats have changed and their effects on each class has been changed. (Strength = Barb, Dexterity = DH/Monk, Intellect = WD/Wizard, Vitality = Health)
- Full stats are now exposed directly on the inventory UI.
All of that is pretty much complete. They are now balancing and polishing and also adding more secondary stats (like + lightning damage, % to find more gold from enemies, etc.)