I have been fishing around and have found out the new path to the SMS bubbles, Send button, and what not. Instead of the bundle: com.apple.MobileSMS, it is now: com.apple.chatkit. You can simply change the name of the folder using SSH if you have a text theme in Winterboard. There is this new image called input-field-cover.png that you will need to make however. Attached is the theme I'm currently using as a template for making your own themes. Enjoy!