Textastic already remembers when the remote file location when you upload or download files and displays this information in the File Information popover (section "Links to Remote Connections"). When you tap on the path, the full path is displayed in an alert.

Or are you referring to something else?
I was thinking more along the lines of showing it for the whole list of files or even being able to sort by it. So often I have several files from one server, or the same file from several servers all in my files list and it's hard to keep track.
Ah, I see. I'll consider it. The problem I see right now is how to fit this information in this small area, especially if a file is linked to more than one remote location.