Best would be a copy&paste system that only supports text, but because people want to copy other crap, you have to support other crap somehow anyway. So yes, you have to add a type to the copied data. But instead of going the way of madness and trying to add a type for every bloody type of data there is, just add two: Normal plain text, and the extended plain text. The second is the file path + metadata (if needed). And low and behold, your copy&paste system is done and finished.
If you want to add network transparency, just copy the tmp file over. Simple as that. The CP system stays the same no matter what data types come and go.
Now instead of picking at unmentioned details, could anyone of you please come with real problems instead?
And no, I haven't thought it thoroughly through. There's no need, as I said, it's trivial stuff, as long as you don't shoot yourself in the foot.