I'd put it at about a 1% chance at best but Lebron would THRIVE in San Antonio. Why? If he came he would already be doing it knowing what he is getting in to. The Spurs have the strongest culture in the league under Pop and everyone knows how it works.
A few years ago I don't think it would have worked but now I could actually see it. Lebron wants to win titles, period. He has his MVP's. He has all the "greatest player in the world" stuff. He has more money than his grandchildren can ever spend. If he came to the Spurs it would be to win. Pop is tough but he is fair and he is deeply respected by his players for his honesty. There is no BS with Pop. He doesn't give a flip about the media. He doesn't give a flip about what people think of him. He just cares about his players and winning, period.
Pop would also get the absolute most out of Lebron while preserving him career wise. There are a lot of places Lebron could go that just want to ride the max out of him they can while they have him. All you have to do is look at how Pop has treated his Big 3 and how well they have aged to see what Lebron could be.
He's not coming though.