It's also similarly likely (unlikely) to occur in the opposite direction (not in any way contradicting your point, of course).

The likelihood of a currency appreciating so significantly against your home currency that it retrospectively makes DCC a good deal is very small indeed. Over time, using DCC will quickly cost more than the (very) occasional 'win' that might come about because of exchange rates changing rapidly an substantially. Far better to stick with the basic rule that DCC is bad for consumers.