So the purpose of such a device is to get data from a real Amiga over to a another computer? This would mainly consist of user created 880k floppy disks, and content stored on an Amiga hard drive?
A600/A1200/A4000 users can already do this with a sub $10 IDE->CF or IDE->SD adapter. These work at the maximum PIO0 rate of the IDE interface and so are quite fast.
But you still have A500/A2000/A3000 & CDTV users who have limited options.
As you say the external floppy disk drive, serial port and parallel ports are common across all.
I imagine that users could put a Gotek floppy disk emulator in an old external floppy disk drive case for a budget solution today?