In a large bowl, whisk flour, sugar, baking powder, salt and baking soda. Cut in butter until mixture resembles coarse crumbs. In another bowl, whisk egg, sour cream and RumChata. Add to flour mixture; stir just until moistened.
Spoon mixture into 6 greased half-pint jars. Center lids on jars and screw on bands until fingertip tight. Place jars in a 6- or 7-qt. oval slow cooker; add enough hot water to reach halfway up the jars, about 5 cups. Cook, covered, on high 1-1/2 to 2 hours or until a toothpick inserted in center of shortcake comes out clean.
Meanwhile, combine pineapple, 2 tablespoons sugar, RumChata and lime zest. Refrigerate, covered, at least 1 hour. Remove jars from slow cooker to wire racks to cool completely. In a large bowl, beat cream until it begins to thicken. Add remaining 1 tablespoon sugar; beat until soft peaks form.
Top shortcakes with pineapple mixture, whipped cream and, if desired, lime slices.