I list 21, since Chris Paul is usually good for 10-15 a year, so he will be up there with the top 15 after the year, almost certainly.
Garnett, Duncan, Dirk, Kobe, all Hall of Fame careers. You can see the clear drop-off from all-time greats to just HOF career (27 Win Share drop to Ray Allen).
James could possibly put up another 18-20 this year, meaning his career would still fall far short of the top 4. he will need 3 LeBron years to get the 50 he will need to move way up to Duncan and KG. Of the guys below LeBron, Kidd, Chauncey, Vince, Brand, Hill, McGrady, Ben Wallace, Andre Miller, Jason Terry are all about shot. Unless LeBron blows out both ACLs tomorrow, they will never catch him. Wade is a great player - 43 Win Shares behind LeBron (LeBron is younger). Nash may play forever, but odds are he cannot play 5 years at the same rate LeBron plays at. Gasol and Marion are still good, but they aren't catching up.
I gotta figure the top 4 guys are capped at around 200. I don't see any of them passing 200, which would mean LeBron would need about 68 more Win Shares to be the winningest of this generation. He will almost certainly do so. If he reaches 201 win shares he will trail only Stockton, Jordan, Malone, Wilt and Kareem.