I think its likely to see cargo and maybe corporate jets to go single piloted IFR (abandon the 12.5K rule) before airliners.
1 - There will never be a pilot shortage at a major airline. There will be a shortage of pilots willing to work for fast food wages...or even PAY to work.
2 - Civilian training is faster but not superior to military flight training. It will always be competitive to get INTO the military. The military doesn't treat their mid-grade officers well which is why there is a shortage of experienced mid-grade officer pilots. If primarily interested in flying go AirGuard first before going regular active duty. A military pilot with 1500-2000 hrs of tactical fighter time is more competitive for a job at a major airline than a regional airline pilot with 10,000 hours as a first officer.
3. 4 year degree required for American, Delta, United, Fedex, UPS and currently SWA. Alaska and Hawaiian are the only two legacy airlines that MAY hire you without a degree but you will likely be a coming from a foreign airline or ACMI carrier like Atlas to get hired.
The big hiring boom will last for 10-15 years and then expect a period of stagnation. The mandatory retirement numbers are pretty staggering over the next 5-10 years. I would expect every military pilot that leaves and every CURRENT regional airline pilot to be able to eventually move to a major inside 10 years. A pilot just starting as regional first officer in the late 2020s will likely be at the regional for 10+ years and without a degree..permanently. Regional airlines understand they are a stepping stone to a major which gives them leverage to treat their pilots pretty poorly.
My advice to your son if he wants to be a pro pilot. Get his certificates and hours as fast as possible and get on with a regional and expect to stay there until he completes a degree. Get a degree that he can use to pay the bills if he loses his medical. I've heard engineering pays well at the entry level.