there are issues with ftp, mostly due to the way the servers are architected. The reason for DreamHost to push for large accounts to move to DreamObjects is purely a technical one: DreamObjects is a lot more resilient and it can keep on growing as users keep on adding files to it. With FTP servers we inevitably hit a limit… I see your profile says you know Solaris and GIS so I assume you know a thing or two about NFS or filesystems in general… Think about the amount of challenges that NFS can give to hundreds of thousands of users accessing mountpoints via FTP, backing those up, moving them when the disks fail, etc To simplify a complex matter, DreamHost founder designed the system powering DreamObject (Ceph) in order to overcome the limitations of storage systems designed for the client-server era.
Can I have a look at your website? Maybe you can setup an application that can interface directly to the object store and offer file sharing capabilities, either via browser or desktop/mobile clients. Collaborators can push data to the object storage system, there are many apps supporting it.
Have you developed the applications that gather data from remote site and push to the website? Which language did you use? are you willing to modify them to use object storage natively instead? The DreamObjects API are quite easy and there are frameworks already, in many languages.