To me, the point of owning a historical replica firearm is to get it as close to original as legally possible. So, for me it would have to be in 8mm Kurz.
PSA is covering all bases with other popular cartridges for people who just want the original look but the practicality of a different round.
Though I think a rail, optics and a "Can" spoils the historical look.
IF the gun is select fire it cannot be sold to regular US citizens who are not licensed machine gun dealers. The smart money would be to make it as a semi auto for general sale, in those states that still allow freedom of choice when it comes to fireams.
The Stg 44 is the original assault rifle, Hitler named it as such, and its defining features are the ones used in the definition of assault rifle (and not the definitions created by US politicians calling them "assault weapons")
If I had the disposable income I would be interested in one (looks like its going to be over $2k when/if they show up), sadly, thanks to too many underinformed people, the magazines are no longer legal to purchase in my state...