I like 1911s, and they are a fine platform, but when it comes down to it, they are too heavy for such an item.
Any Soldier will tell you that ounces equal pounds. Reliable lightweight gear in the field when YOU are carrying it is critical and can mean the difference in YOU succeeding or failing.
Nearly every piece of modern gear is replaced with light weight metals and plastics where possible. The empty 1911 weights like a pound more than a polymer handgun. Those pounds add up fast. That pound could be replaced with extra ammo, water, food, medical supplies, body armor...
Agreed, that a handgun is an emergency tool for a Soldier in combat. It's a last line of defense. Therefore, I also have issues with the .45 ACP for that role. Capacity is more important, and I'm okay with the 9mm, especially if we could use hollowpoints.
With regard to the rare situations where the 1911 was successful at a last line defense, like SGT York, consider he was fighting against Soldier with full size slow bolt action rifles. Killing 6 men at close range who are using bolt actions weapons, when you have a 8 shot .45, is fantastic, but would not be impossible - as demonstrated. Now, consider if those Germans had semi-auto SKS rifles, or AK47s... and sadly SGT York and his 1911 would have died in place and never recorded in the analogues.
Similarly, I be there's lots of examples we just never heard of where the 1911 shined and defended against 8 attackers, but attacker number 9+ managed to kill the Soldier and we'll never know about it.
Modern tactics change because modern fighting has changed. Holding onto the 1911, a weapon of yesteryear, is simply foolish. Again, I love the 1911, but accept it for what it is. Just like I love the M1 Garand, but nobody would seriously consider implementing that again, today, as a front line weapon.
Given all this, the 1911 still shines in the role for home and self defense, where you aren't being overrun by enemies after/during a gun battle.
But all of that said, I would not pick a 1911 as a first line pistol for modern combat roles; I would pick a lighter, more reliable, 9mm such as the Glock 19 and 17. It offers the most important features of reliability, light weight (gun and ammo), high capacity, accuracy, and the minimum acceptable caliber.