A couple of things - one, the FDA has approved a cannabis derived CBD drug called Epidiolex. This is one reason that the Sch. 1 listing does not fit any longer; indeed, our government has found a medical use for cannabis in treating pediatric seizure disorders. Epidiolex had to be developed by a non-American company because of it's Sch. 1 status - it is next to impossible to do research on different cannabis strains in America. So when people say "it hasn't been tested" its kind of a catch-22 because it cannot legally be tested. At least as long as it's on Sch. 1.
Popcorn lung has only happened in black market vapes where the formula is adulterated to cheapen the production costs. It does not happen with commercially available nicotine or cannabis vapes (at least in states like CA where there are strict standards for production of cannabis products), without someone breaking the law.
But I wouldn't rush out to start vaping if you don't already. My advice is that if you don't smoke, don't start. If you smoke cigarettes, see if vaping nicotine suits you better. It's 95% safer than cigarettes according to Royal College of Physicians in the UK, and is very successful as being the bridge between smoking and cessation of tobacco products (much more effective than gum, patches or other smoking cessation products).
Marijuana remains illegal at the federal level and ports, being "ports of entry", can and will arrest people for possession. It doesn't happen often, but it is possible. Many people get away with cannabis vapes as they don't smell, don't look any different than nicotine vapes, and are not as obvious as a bag of weed. Easier to smuggle and get past CBP are cannabis oil capsules that are indistinguishable from Vitamin E capsules. But, you are taking some risk of arrest and prosecution for possession of cannabis.