CF nylon is nice if you’re trying to print an OEM quality frame but not truly necessary. $100 3D printers, out of the box, will print PLA+ which is absolutely strong enough for 95% of modern printable designs. Some designs, like the 3DP90, NylAUG, Orca, etc require some non-PLA parts but I digress.
The downside to PLA is also what makes it so easy to print — it can’t handle prolonged heat exposure. PLA printed parts will often warp if left in a car on a summer day. Anyway, there are also printable lowers for ARs that are extremely reliable (UBAR2, Hoffman, etc) along with plenty of shops that will happily sell complete uppers.
As for regulating parts kits… a high profile case like this could motivate a nationwide push. But self-made firearms are as American as apple pie and something we’ve done since the earliest colonial days. There are a few states that have passed laws against self-made firearms, but it’s legal to make your own gun in the vast majority of states.
‘Murica!