I'm reading this in fascination. I'm a struggling learner, getting better, but I HATE cold water. My first real open water tri was and Olympic distance in glacier fed Two Jack Lake in Banff National Park; wet suit, but overwhelming for a fledgeling swimmer. I thought I nearly died. I was the last out of the water at 46 minutes actually there was one guy after me but he was pulled into the medical tent with hypothermia -- why I didn't get hypothermia myself is beyond me -- I'm really skinny.
I've improved my swimming since, but I still hate cold water, and I think I would be too distracted training in cold water to be of much usefulness.
My latest challenge is a cracked or badly bruised rib 2 weeks ago. I find the pain so distracting that it's hard to get any good well focussed technique practice for long. But I'm sure I would find the cold even more distracting -- I find it difficult how you guys can focus on technique when your body is hurting from the cold.