There's nothing wrong with your idea, but the hardware must be able to work with some badly written/designed software. The speed problem has already been mentioned but using cracked ADF's would fix most of them. Another problem is that many games come on more than 1 disk and the software is expecting a physical removal of the disk then reinserting. That would have to be done with a manual button press on the device unless you want to change the software.
On the plus side of things most of the floppy drive logic would already be known by the programmers of the Amiga emulators.
Maybe another solution would be to connect the Amigas floppy port to a PC which would be used as a slave device serving floppy requests? All that would be needed is an old 286 (or maybe even an old XT) with a hard drive which surely isn't worth much these days. The problem would be writing the software which is necessary for the memory card also. I think this technique (using PC as slave) has been used with Commodore 64's. The disadvantage is the space and extra power required for the PC. The advantage is that the hardware is available, reasonably cheap and there are many with the necessary programming skills for the job.
I guess the question is: Is there enough demand for this feature to warrant the effort?
* If you used a more modern PC you could also get it to play a selection of your favourite MP3s as backing tracks to the games