Not popular as you say, but may be pragmatic. Allardyce is one of those characters that is easy to poke fun at, and appointing him would represent a bit of a kick in the teeth to Moshiri's talk of ambition, but as they say, if needs must, then needs be. It absolutely depends on how long the slump goes on for under Koeman, and what state we find ourselves in if and when he got the sack.
Hard to define how close is too close for comfort for relegation, but if we are having that conversation at Christmas, then it's an absolute full-blown crisis and no better than Allardyce in that scenario to get us out of it. I very much doubt he would sign a short-term contract though and wouldn't blame him either.
If he ever got the job, it would be under those circumstances I think, meaning we faced a genuine battle for survival. But I really can't countenance Koeman struggling on for more than a couple of weeks if we lose the next 2. I'm pretty sure that would mean Unsworth being asked to step up.