Nalgene claims their cantene soft bottles can handle boiling water, and they have wide mouths . . . I've read on BPL that some people use the platapus bags without issue, although the narrow mouth may be a bit awkward to poor boiling water into.
I use a wide mouth nalgene polyethylene bottle, BUT, boiling water is darn hot and an uninsulated bottle cools down pretty fast. Many people use a cozy for their hot water bottle that keeps it from being so hot it burns, AND keeps it warm much longer into the night than an uninsulated bottle would.
I'd love to know how the nalgene cantenes hold up to boiling water over time.