@hongminhee like I mentioned in a thread where Evan and Reiver were talking about this, I think having a mediaUpload that has a very similar behaviour to an inbox/outbox, but with one **small** changed detail is a bad API.
I would prefer there's either a two step process: upload media first, use resulting token in an object create, or use the outbox with for the binary data upload directly... The first one seems saner to me.