I've never seen a soft drink sweetened with Xylitol. Is this a store brand thing? Most soft drinks I encounter seem to be sweetened by a combination of aspartame and acesulfame K.
Xylitol seems to be common in candy (especially chewing gum) and deserts, but I don't think that's relevant to a soda tax.
Perhaps you know of a commercial soft drink sweetened with xylitol that I don't?