I did not notice any security issues with this document, and the security considerations section seems straightforward.

(nit / question / feel free to ignore) I was a bit confused by the term "HTTP extensions" at first, but from context, I'm guessing it's used loosely to mean any addition to HTTP? I found RFC 2774 when I was looking to see if it meant something specific, but I'm guessing it's not a reference to a 20+ year old experimental RFC?