For Buffers, set the content type to application/octet-stream by default.

When buffers are attached to a form they were added with no content type; therefore, the content type would default to 'text/plan'. This modification changes this behaviour to default to 'application/octet-stream' for buffers.
The user is also able to add a 'filename' optional field to the header in case a file is being sent in binary form.
Quote: "As of the publication of this document, there are no standardized Internet transports for which it is legitimate to include unencoded 8-bit or binary data in mail bodies. Thus there are no circumstances in which the "8bit" or "binary" Content-Transfer-Encoding is actually legal on the Internet. However, in the event that 8-bit or binary mail transport becomes a reality in Internet mail, or when this document is used in conjunction with any other 8-bit or binary-capable transport mechanism, 8-bit or binary bodies should be labeled as such using this mechanism."

And it seems like they very concerned about mail transport in the future, I don't want to sound Bill Gates here, but I don't see using form-data@0.2 to send emails.

And my main concern, that if it does make the difference (not yet so far) it will introduce different behavior when you send binary files and binary buffers, which is totally unexpected from user's point of view.