I'm finally getting a carbonator to try this out. I usually like my coffee hot and flat, roasted 24-72 hours prior to drinking, but have had it as a cold brewed coffee before.
While I've not tried it out using cold brewed coffee, I imagine that the french soda type of drink would work well with a coffee flavor already. (Generally it's syrup, carbonated water and cream or half&half).
Most reviews for carbonated coffee drinks don't seem that well off and I can't seem to think of any other situations I'd wind up using a carbonated coffee drink for, even as a mixer. Maybe with a small splash of Vanilla Vodka over ice. (.5-1 ounce per 12 ounces of coffee) for flavor. Although... A coffee float does sound pretty appetizing. Coffee soda, possibly unsweetened and a scoop of vanilla ice cream? Or Chocolate Ice cream?