I never thought about the 2nd Scimitar possibility. That's a very interesting idea. My first reaction was "Yeah, you could act with the Mage, attack with the Scimitar, Quick Cast another Scimitar, and attack again." But then I reread the Autonomous description.
Unlike similar effects which say "after the creature's action phase" the description for Autonomous says "at the end of the creature's Action Phase." This very well might be splitting hairs, but it does leave some room for doubt. It's possible that the Scimitar's attack is considered part of the creature's action phase still, and after that has been done and the Action Phase is over with, you couldn't use another Scimitar.
Again, I'm not certain how to rule this one. I don't think Quick Casting a 2nd Scimitar is any more powerful than a Flameblast or similar spell, so I don't see any reason currently to disallow the tactic, but I did want to point out the possibility that it might not be allowed. It all depends on how you interpret "at the end."