Most rooms don’t need acoustical treatment.

Oh, dekay.....*sigh*  'Fanny packs' (aka 'butt bags') are So 20th Cen....

Spouse remembered a wool vest I wore decades ago (until the dry cleaner shrunk it to fit a 3 yr. old).....and got me this recently...
https://www.scottevest.com/shop/mens-vests/mens-fleece-vest/fireside-fleece-vest-men.shtml
Comfy, but I'm prone to 'frisking' myself trying to find whatever I'm trying to find...and you'll note it has the Least pockets of their products....

My 'listening space' is a little better than you've illustrated (no search parties required as yet), but is cluttered enough that I'm looking forward to the day it becomes obsolete due to a relocation.
But, since I run DEQ, it sounds good to my drain bamage....for now. *S*

Something I've considered, since I'm an omni fan, is to investigate trying these as a surface over an acoustic 'blanket/panel'....
https://www.homedepot.com/p/Art3dwallpanels-19-7-in-x-19-7-in-White-PVC-3D-Wall-Panels-Wavy-Wall-Des...
...if only to avoid the 'padded cell' look of an extreme acoustic treatment, and keeping in mine that omnis 'like' reflection...properly attended to, of course....;)

Thinking 'outside the box' first requires one to accept the existence of 'the box'...
I've tended to lean into a 'mobius loop' sort of reality, myself...*G*

@sandthemall.....
Another ’off no wall in particular’....

sand them all -or- sand the mall? Either makes sense to me, but just obliquely curious....*G* ;)

'asv', for me, is just my variant on AVL (thinking that all caps would be too big of a hint....*L*)

geof3, you are right, I reread the original statement.

Sum all untreated rooms and they average out to have random placements of objects made of random materials.

Ampa style setups need close to nothing. No back wall and tapered side walls and ceiling, no reflection points..

Setting up kitty corner, eliminates a lot of the normal treatment ideas and again the reflection points diminish. Room decay rates are much quicker.

Clutter counts :-) There are ways to reduce the UGLY as$ wall treatments diffusers, dust collecting stuff. Foam is hard to keep clean.

CURTIANS work and look the best to me..

It's easy to tune a room and liven it up just a bit with a curtain pulled open or closed a little more.. No studio looks for me.. 

Regards