Being a Yankee who has now lived in South Carolina for 12 years, I think I finally have "might could" figured out. "Might could" means "I will put that on my to-do list somewhere around, oh, #37. And if you never bring it up again, neither will I." "Might" means they could be cajoled into it, or that there may be time constraints involved in being able to do it. "Could" means they are capable of doing it. "Might could" expresses a level of ambivalence to doing it that using either word singularly does not convey. It is an awkward construct, but it does have a meaning, bad grammar be damned.