Depends on the pro apps.

In the age of iCloud, Dropbox, and 200 other services and alternative ways to move stuff, why would one want to use a FTP client (like the Transmit above) on the iPad?

The market for FTP clients is small enough on the desktop...

(Heck, I'm a developer, I have a Transmit license since 2006 or so, I work with dozens of remote machines, and seldom ever use it. It's either sftp on the command line, or something like an Ansible wrapper etc).