How can you say he didn't leave the baseline? Does the baseline extend all the way into the outfield? He was past the base and the next base is a totally different direction than where he was going. While I get the whole direction going into the base is the established line to determine if someone is avoiding a tag that does not fall under this. He's no longer in the basepath because he's no longer attempting to go to a base.
I think the slide that took out Kang was a good one. It falls within the rules of Coughlan can reach the base and Kang has a chance to protect himself. If I remember correctly this was another situation where it was a slow developing play and Kang shouldn't have tried to continue on to first. If the fielder is beside the base then the runner should be able to slide past as long as they are touching the base. If that happens the fielder has the chance to see what's happening and make a decision to protect themselves or try to continue. If the fielder is behind the base then you are targeting the fielder.
So, then how do you define going past the base? How about the runner stealing 2nd? He goes beyond the base with all of his body, except maybe touching the back of the bag with the tip of his toe. Is this going beyond, or should the rule be that you can go past the base, but still be able to touch it from the other side? Also, the baseline is established by the runner as he heads towards the next base. If the runner is not heading towards the next base, technically, there is no baseline.
How bout the runner that runs past 1st base on a ball in play to the infield? Should he be called out because he went past 1st base, but not towards 2nd? More to think about than what initially comes to mind...