I don't think the likes of Allardyce or Ince will come, but it isn't a complete non-starter and IMO dismissing it out of hand is just silly. Here's a precedent...
Allardyce is a big name. Keegan is a bigger name.
Allardyce was sacked from Newcastle. Keegan resigned from Newcastle.
Allardyce got Bolton into the top six. Keegan had Newcastle in the top two.
So, Keegan's stock was considerably higher than Allardyce's.
Yet Keegan then went to Fulham, for the money. Fulham were a much smaller club than City are now, in the equivalent of League 1.
People often talk like they know these managers personally - oh, he'll never come here! How do you know what their frame of mind is? Allardyce has been successful at small and mid-sized clubs but fecked up at a big club. Who knows - we might be just what he's looking for...
As I said, I think it's pretty unlikely, but if you don't ask, you don't get. If you aim low, you'll get crap, guaranteed. IMO we might as well try and hook the biggest fish available. What's the worst that can happen?