Interesting, the added apple cider vinegar. Might try that. I've got a pint jar of canned mountain huckleberries, been wondering what to do with. Cocktails it is!
Not that I’m usually that organised, but ppl do things like macerate berries in apple cider vinegar for 48 hrs, then stain it off to make a shrub. Adds real depth of flavour. You’ll still want some added syrup/sugar of some kind to balance it. Make sure to get the cloudy vinegar with the ‘mother’ in it. It’s the real deal. Keeps for years too.