Changeable barrels is pretty neat. The barrels are either 16" or 18"....I'd think a 21" or 22" would be minimal added weight for someone not planning to run a suppressor.
No brainer to go AICS mags.
Make a small bolt face available so the barrel can be swapped out to a .223.
I didn't catch how long/short the LOP could be made but adjustable is always nice, especially with kids growing.
