I wonder if it might make sense to have most of your water bottles be plastic and have one that is metal. Save you a lot of weight and some cash.

The wire bail is a good idea. How it would fold and be out of the way, I'm not so sure. Unless your bottle has a metal lid, you'll need to remove the lid for heating. What if you just brought an ordinary pot gripper of the type used for backpacking? You'd lift the metal bottle out of the fire just as you would a pot used for cooking. Might be less hassle than a wire bail although a wire bail has the obvious advantage of being able to be suspended over a fire from a stick.

HJ