Is it really the ultimate defense gun?
As much as I enjoy watching shotguns blast clays at the range, blow up jugs of water at the dump (growing up), or even watching the guy next to me at the indoor range rip apart paper targets - I still understand that it is just another tool to employ for many purposes, to include self defense (Force Protection).
1. Limitations of welding weapons of such size and weight - concerns for quick in the dark movements to safe areas, running, riding, moving in and out of crowds, etc.
2. Limitations on number of rounds that can be fired prior to reloading.
3. CEP - many divergent projectiles as opposed to the single projectile (both a strength and weakness). Obviously all those projectiles do not discriminate by intent to only harm the intended target(s) (presumed to be the bad guys).
4. Overpenetration is a huge concern with most shotgun loads (walls, doors, windows,etc.) - these issues remain with any vectored metal object(s) (high velocities in a directed path).
The place where the engagement is to take place is really up to the bad guy(s). They strike people at home, on the road, at National Parks, etc. I don't know if the shotgun as the "ultimate defense gun" is practical to be in all these places up-and-ready to employ.
As far as the psychological aspects of facing an adversary with a known shotgun capability - I think a known unseen adversary (stalking) not flashing a weapon or making extra noise with a weapon can be more of psychological distraction for an adversary. Better yet, an unknown unseen adversary (to the BG) stalking where the bad guy is in even less control of his/her fate. But I do not want to make any overstatements as every situation is different and perhaps there are appropriate times challenge others with noise, etc.
As far as defense goes - it is my opinion that it must not dwell on the "ultimate" anything but can be accomplished by mapping out and drilling through a fire employment / fire support plan since much of the terrain I'm hearing in here concerns home defensive postures. Movement and maneuver, communication assets (whether to LE (so you can produce even greater pressure on the BG and limit the time you may be dealing with the BG alone), as well as other team members, etc.), safe areas, and many other TTP's guided by METT-TSL analysis can provide much more enhanced force protection than dwelling on a single type of firearm/weapon.
In many cases I'd prefer NODS and a silenced .22 (especially if I'm defending home turf or territory I'm both familiar with and have prepared for such engagements) than a shotgun. I'm sure most reading this have such a plan and consider their own version of unit (family) SOPs and ROE so that when fires are necessary there is a lower risk of fratricide.
IMHO effective defense is not about the weapon but about the overall plan and therefore the ultimate defense gun does not exist...