Oh, wow, I think I see where you are going. Like a the cheapie travel mugs that have the removable bottom so they can be cleaned, but made out of stainless and lacking the handle. Maybe use something like styrofoam or fiberglass insulation in a plastic sheath as your removable inner insulation but that wouldn't be critical.

Have a screw on bottom and a screw on top. Heck, it might be possible to make the bottom wide and deep enough that it could be used as a small bowl or large cup. You'd want to be able to be compatible with the standard Nalgene cap so you can use all the various filters out there. And if it's shiny, it would work great with the Steripen- UV bouncing off the sides rather than going out the bottle.

It wouldn't be a field conversion, but I think you might have something there.