The problem with FTP starts with the protocol. It's tragic that this startup doesn't use something like SFTP.
1FTP looks like it has a nice interface though.
That wouldn't solve the shared account credential problem that 1FTP tackles, but it would improve security.
It may not seem so to an experienced developer, but the experience for an end user with things like that is an absolute nightmare. We're trying to make it easier, not harder :)
There are some good GUIs for SCP that reduce the barriers of entry to the same level as FTP.
IMO you're trying to solve a problem that shouldn't be solved. Maybe turn your 1FTP app into an SCP interface. That way the "difficult" things you describe become easy.
My hate for FTP could be clouding my judgement.