I don't think Klopp wants to consider Lukaku because Lukaku seems not suitable with Liverpool game style. Liverpool is looking for a typical player that has a similar characteristic as Mane and Lukaku is clearly not the right option. Nunez is a good option to replace Mane's role in Liverpool squad although his transfer fees are quite expensive. And Nunez is still a young player who can play a long time.
His vision of the game doesn't really match Liverpool, why should it be forced, even though in this case Liverpool still have many options for attackers but I don't think Klopp will make a choice for him, especially for Nunez, soon the contract talks will be completed.
Most likely Lukaku will rejoin Inter Milan.