How will that prevent bots? They have always been a problem and will always be a problem. Adding a check for a soulstone isn't going to stop the problem of bots in dungeons. You build a better mousetrap, they build a better mouse, etc. Then they go and get the level 30 soulstone and never do another quest again anyway.

Personally I'd rather SE focus on making the game a better experience for the players than spend all their time devising more restrictions in order to combat bots. I know it's considered a radical idea to some, but if gil wasn't such a big deal in this game (meaning certain sellable things being so rare that they end up priced extraordinarily high) then bots wouldn't have a job. As long as SE continues to treat the economy like they do, players will want to take shortcuts to earning gil to afford the things they want and can't get, and bots will continue to exist to farm gil.