I mean, it's completely outside of viability, but it's not breaking ground science. You could do it perfectly well in a lab (if you had any reason to).
There's a lot of things that can be done in a lab, but bringing it to the real world is totally different. Nevermind fitting this in the original concept of backpacking
You can turn methane into water in theory. And you can technically do it in a lab (even though the easiest way by far to do it uses a lot of water). You can't do it on your backpack.
You "just" have to capture and cool it down.
I mean, it's completely outside of viability, but it's not breaking ground science. You could do it perfectly well in a lab (if you had any reason to).