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.
Lukaku is a good player but the EPL is not a friendly enough league for this player, how many clubs has he been to and only at Everton did he play well but for big teams like Chelsea and Manchester United he can't do much there.
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.
Besides the fact that Lukaku has proved to be a very unstable player... we must remember that he arrived at Chelsea as one of the great strikers in world football. After shining with the Milan shirt, Chelsea paid 113 million euros for him, however he ended up being a disappointment, would Liverpool be different? It is risky to make this prediction.
I think a more certain destination for Lukaku would be to return to Milan.