I only get my Milkis from the most authentic sources - from a GS25 in Hongdae at 3am, stumbling in after several drinks and a pack of long island iced tea cigarettes smoked in the club, paired with a bulgogi kimbap
Well... The sparkling will be really intense and short-lived, as all that carbonic acid reacts with the bases on the milk. Then it will be completely flat.
Also, from the taste of old tooth-paste, I imagine CaCO3 tastes like spoiled sand would if sand was capable of spoiling.