Hi Sebastien, I have encountered issues with this before when trying to noweb code into a string that was code to be sent via ssh. I ended up switching to use typeset -f in bash in most cases now, but that is not possible for other languages. Some languages also have enough different types of syntax for strings that they can work around such cases, but again, not all do.
One potential issue with this suggestion is how it would interact with multi-line blocks, because you can't have anything on the same starting line as the noweb expressions since it will be repeated in front of every subsequent line. This would also require each org-babel lang implementation to provide a method for correctly string-escaping the nowebbed values (in some cases e.g. shell this is decidedly non-trivial). With all of these things in mind, I would thus suggest not trying to overload the noweb operator for this purpose. Having a string escaped equivalent would be nice, but because it requires more than just a simple copy/paste into the buffer, it seems like it probably needs separate notation. Best, Tom