I'm not sure how that would help.
Help who? It was mentioned that Southampton had a similar system and it helped them with getting Koeman when they replaced the guy who went to Tottenham. It can't be a bad thing having a list of ready made replacements should you need to replace a player or coach or whatever. Of course the trick is having the right DOF to who is able compile a database of decent talent and not just any random names. It seemed to work for Albion while Ashworth(?) was at the club.
Were all 15+ names available or reasonably attainable? Were they in any particular order, perhaps quality, chance of actually getting them, age, cost in salary, cost of severene, alphabetical? How often should the list of candidates be reviewed as their form and value changed with the passing of each game? Do we know Villa don't have similar lists? If not, how long would it take to compile a decent sized list. It shouldn't take more than a few hours to come up with possible candidates.
Having a list ready (and we don't know Villa didn't have a list) really doesn't help much. You could have a list of a 100 and still pick the wrong manager or not have a list ready, compile a shortlist over a few days and end up with the right man.