We can outlaw it, but we are building a spec which allows one to put
an arbitrary file into a part of a message. People will do this to
mail files. Gateways will be programmed to do it too.
Why do you want to outlaw this?!?
In the current implementation of the world there is unequal access
to all parts of the world. Namely: ftp doesn't reach everywhere.
It reaches lots of places, and it is reaching more and more places
every day. But in no way does it reach everywhere.
So of course people need to send files through e-mail. Either ad-hoc
in a person sharing files with another person, or an organized archive
server along the lines of BITFTP(_at_)PUCC,
Also e-mail is more convenient since it already has nice failure
detection & retry & queuing mechanisms built in while ftp does not.
Given the `multipart' stuff in the current draft we can even make it
handle flaky network sections without large cost.