There isn’t a way to ‘ban’ JSP. The only thing Blizzard can do is to bring a better in-game centralized trade function to the game. Something good enough where people won’t need to use JSP, and other centralized trading forums to trade, which also reduces or eliminates the chance for scammers to do their thing.
Sure you’re going to have holdouts that will still use JSP, because they’re heavily invested into it.
Me, I don’t use JSP. I still use the archaic limited trade function the game offers. Create “X 4 Y” games, or browse for “X 4 Y” games.
Bring on the trading post, Blizzard.