Personally I don’t think that adding another Detachment is the solution, because of the nature of the costumes that would reside under the “Imperial Army” Detachment. Let me elaborate on that by smashing my keyboard a bit and throwing some copypasta.
The Wookieepedia says;
”Imperial Army troopers, also known as Imperial Army soldiers, were the standard soldiers deployed by the Imperial Army as the infantry component of the Galactic Empire throughout the galaxy. Those troopers, who were separate from the elite white-armored stormtroopers and the fleet troopers of the Imperial Navy, were formed from eager and often young conscripts, serving as expeditionary units tasked with the subjugation of worlds that dared to resist the Emperor's rule.”
Which would make them a specialized unit that are only used on specific locations; Ryloth, Aldhani, Mimban and Marca. The other two troopers that are mentioned already have a clearly defined Detachment within the 501st Legion Detachments (FISD & IOC).
When the Star Wars TV Series/Stories are finished with the Empire era and Empire has been defeated, nothing new will be added to the Imperial Army Detachment and the Detachment will see nothing new added indefinitely.
I think that instead of going through the difficult and long road of forming another Detachment, It might be a better idea to see if we can redefine what the Special Operations Detachment houses, because I think that the Imperial Army Troopers are all specialized units that would fit in well within the bounds of such a Detachment. None of these army troopers will be seen on terrain that they’re not equipped for. It would make them a type of Spec Ops costume In a similar fashion we see Shoretroopers and Scout Troopers being listed on the Pathfinder CRLs, Officers, Crew and Navy on the Imperial Officer Corps CRLs just to name a few.
