The issue is can they be made at a reasonable enough cost to make it worth doing?
It would cost a ton because whoever attempts to build it would essentially be doing it from scratch. Unlike AR's and AK's which can be slapped together using parts made by the millions over several decades from a dozen different sources, the StG-44 has for all intents and purposes been extinct for a long time. A would-be manufacturer would have to re-invent the wheel and make every last part themselves because there's nowhere else to source anything from, all contributing to high R&D and manufacturing costs.
Evidence of the fact can be found by looking at the mags; even modern reproductions of StG-44 mags sell for around $150 a piece when you can find them, I certainly wouldn't expect a modern repro StG rifle to sell competitively against AK's or even AR's (both of which are technically superior weapons to the StG-44 and thus eliminate any practical reason for wanting one). There are of course impractical reasons for wanting an StG-44, such as the novelty of owning an StG-44 clone, but will enough people be willing to fork over a $2,500 for novelty?
"My momma, she done told me, there's heart and then there's hate
If one of 'em's inside of you, the other one, it aint."