First, I'd like to amend my definition of airplane to:

(*) Airplanes defined as vehicles which rely on aerodynamic lift during all phases of flight, and do not acheive altitudes that count as "space".

Just in case we switch from jet engines to something else. But I still think most people will be travelling via aerodyamic lift at non-hypersonic speeds.

Why am I confident?

Three reasons. On the engineering side, it really is a problem that gets tougher as your speed increases. SS1 is *not* halfway there, or even 1/10th of the the way there. That awful rocket equation plus the reentry heating problem means the problem isn't linear; almost orbital is a lot worse than duplicating a V2. And I suspect those performance demeands will have implications for operating costs/reliability even once you've got the R&D done.

On the economics side, it's not hard to see why people would pay more to get from LA to NY in six hours instead of five days. But 1 hour vs 6 hours in transit? Especially since that probably means 4 hours vs 9 hours when considering local ground travel, ticket processing, loading and unloading, security, etc. SEveral days is meaningful on a human scales; a few hours not so much to most people. If it mattered so much, why aren't there a lot more non-stops between LA and NY? Plenty of people are willing to lose 2 hours or more changing planes enroute.

On the alternatives side, I bet virtual methods will continue to improve. SOme sort of 3D videoconferencing wouldn't be any harder to develop than practical suborbital passenger service. Or having a brain implant that you can remotely connect to a droid on the other side of the country, acting as your eyes and hands there.

I'll grant that by 2036 I could see a small market for suborbital transcon flights -- and military applications of course -- but I just don't see it being the preferred method of transport, not by a long shot.