Lebron James is 39 years old and his career is not long anymore. with high contracts and salaries it will be difficult for new clubs to accommodate him. because there are salary cap rules, aka there is a maximum budget limit for each club that can be spent. so if there is a club that wants Lebron James, they have to sell or throw away their star players so that the salary cap spot is there to accommodate Lebron James.
In terms of having someone like him to their roster before his retirement is like some sort of history. But what most teams like to have history is to win championships. Each team has their own franchise and best player that they can have and give the salary cap.
While it is not going to give Lebron that much benefit but AFAIK, this is just a rumor and won't happen.
I also think that no matter how much you pay for a player like Lebron, you make that money back easily. Since there is a cap on how much a player could get, in order to make sure that other players get paid decently as well, and there is a cap on minimum, so that no player gets too little and make it a bit more equal.
This causes players like Lebron to get paid not enough, and teams who pay the maximum they could offer him, would get that money back. Just the fact that you would get sold out seats, with probably higher ticket prices, for people who will come out to see him. This means that if he ever decides to leave, then he is going to end up making a team a lot of money, even increase the value of the team for a while as well.