id make avordable piston conversions for ARs. theres a huge market for them.
You think? The military is very unlikely to convert on a large scale - I've seen a whopping total of two
HK416s here, both with SEALs. It's not like AR-pattern guns in civilian service see the hard duty that would make a piston gun worthwhile. American cops and citizens have plenty of time to clean their impingement guns and keep them reliable.
I think the piston guns are a pretty good of example of supply creating an artificial demand, or, as Jeff Cooper might have said, "a solution in search of a problem." Yeah, they are the rage in gun magazines, but gun magazines exist to help sell advertising, and makers of piston guns all have marketing budgets. AR hobbyists are over them like stink on a bug, but some AR guys by their nature always latch onto new stuff whether they need it or not - look at all the guys with $600 Surefire lights on guns that only come out of the safe to go a range in broad daylight, or the guys with bipods and ACOGs who never shoot anything father than 100 yards. But guys this serious about ARs aren't all that common, though I guess maybe they'd be more so if the price of piston uppers was more reasonable.
As for me, I've always thought a neat gun would be a 5.56mm semiauto carbine about the size and general shape of a Mini-14 that accepted 10-round en bloc
clips and mounted a low-powered optic forward of the action. Add a good 4-5 pound trigger and a safety better than the Garand style, and decent backup aperture sights. You'd have a 50-states legal defense carbine that would be easy-handling, easy to shoot well, fast to reload, relatively cheap to shoot, and use inexpensive clips instead of magazines. Maybe make it in stainless for humid environments, and explore making the clips from polymer instead of metal.