I've looked at it. It shouldn't be too bad as the core complexity in the FlickrNet library is done using XmlTextReader, which is still part of the Metro profile.
The cryptography bit needs changing as System.Cryptography has gone, but I've already worked that out.
So the rest is probably just changing all the async calls over to use the async/await keywords, which will be quite a bit of work but not that difficult.
However I'm in no rush to get it done I'm afraid, as I don't have the bandwidth at the moment. If someone else wants to look into it then feel free.