I would prefer some balance changes, rather than new content.
Remove immunities and make mobs/bosses tougher to compensate (increase hp, keep high resistance but not immune) this would unlock a lot of more builds which don't require to break immunity and this would already make game a lot more fresh because you can experience the game with builds you never could.
I would be careful with buffing and nerfing abilities, that could fuck up a lot , but I would welcome some rebalancing, just for the love of god, don't touch items.
Creating new content requires too much development time and it might be weird to do that since we already have a game for time between D2 and D3