That's a great idea but I don't think that it can be done. I just checked the API doc and came across this post:
https://groups.google.com/forum/m/#!msg/google-chrome-develo...The post is from 2013 and the documentation doesn't clearly say that it's not possible, so there could be some hope... That being said, one could find some work-arounds to make something work even if not as nice as an item in the contextual menu.
E.g. It looks like an extension can read and write the clipboard. Then you could have an action button that just converts the cURL command in the clipboard into the Requests one. Or, more agressively, poll the clipboard and replace any cURL into Requests...
Right now, I can't think of a UX as good as a context menu in the networks panel: having an action button all the time just for that would seem like a waste of space, a DevTools tab as well, a context menu item only present if the clipboard is a cURL command would be fine because present only when needed however it'd be out of context...
