Having spent 35 years as a desing engineer at Boeing, I found some of those ideas laughable.

An aircraft is a closed cylinder that recycles over 50% of its air. Fill it with pepper spray and it isn't going away! Everybody in the the plane will be subjected to excruciating pain for a long time. People with breathing problems or bad hearts could die. Accidental discharge is a far more likely occurrence than a hijacking. The
cockpit air comes from the same source.

The weight of a parachute and the resultant structural reinforcement to attach it would be the equivalent of several passengers. Again, the risk of accidental deployment or engine shutdown is higher than hijacking. Rather than remove several passengers, I would fill those seats with gun totin' sky marshals.

It would take too long to comment on all his ideas, but the fact that, as he says, no one from positions of authority such as the FAA or aircraft manufacturers have contacted him, may indicate the validity of his ideas.