I'm sorry but given the paucity of background information submitted by the OP, it's difficult for me to give any consideration to his question. And no, I'm not mocking him, as a mod suggested in the other thread.
In order to even seriously entertain discussing this idea with the OP, once again, he should express
why he would want to carry such a weapon in an urban/suburban environment. Even putting aside the question of
need. because if there were any urban/suburban areas where any of us average citizens
needed to carry a weapon in this manner, we'd already know, right?
Given that this member has offered up exactly zero information on his background, level of training (may not be important to some of you, but if one is going to go forth armed in this manner, one better have some significant training), or (importantly) location -- which certainly has a bearing on this topic, as cities/regions throughout the country differ widely with regard to firearms laws, permissive/non-permissive areas and the general culture/acceptance of firearms.
As others have noted, a citizen in civilian clothes -- with no law enforcement markings on body armor or a jacket and no visible badge --pulling a weapon out of a backpack in almost any possible scenario in which gunshots are heard --- will certainly be taken down by the first responding law enforcement personnel on scene.
I personally see no possible good outcomes for the average citizen engaging in this type of firearms carry. It's already dicey enough out there for law-abiding citizens who defend themselves with concealed handguns. Unless we're talking a
Red Dawn, Invasion USA or
Walking Dead situation...
For me, if I'm going anywhere other than the range with a long gun (even a breakdown carbine or SBR), I'm wearing a ballistic helmet and glasses, body armor and Level IV plates with, as mcb says
as many similar equipped friends as I could find, and maybe some armored support, and air cover while we are wishing...