I'm also an "aerospace veteran" and have seen more projects cancelled than succeed (most recently the Lear 85). Designing a new plane is capital "H" Hard. That goes doubly so for planes that are big departures from the previous experience of the company. Cessna makes great light business jets. They are currently trying to design a line of bigger jets and are finding it very hard. Lear can't figure out how to make anything without mechanical flight controls. It takes a couple generations of design to figure things out. So a bunch of engineers from Scaled and Boeing aren't going to help. How many ex-Concorde engineers have they hired?
All right, when you said you are an aerospace veteran I was prepared to take you seriously, but this cancels that out completely. Firstly any Concorde engineers would, if they started their career right out of college on Concorde, be about 80 years old by now. Then this plane is using different and much more modern engine technology, different control systems and different materials. Almost nothing learned from Concorde would be up to date and relevant to this plane, from an engineering perspective.
We should remain skeptical whenever someone says they will do great things that hasn't been done before, but immediately going to the conclusion of "it's impossible because I can't imagine how to make it work" is just plain arrogance - a true skeptic should be skeptical of his/her own judgement.
What? I don't think that has anything to do with it at all, and the distinction between types of engineering seems irrelevant. I think he's pointing out that they're trying to make a profitable business without understanding the necessary costs. Given the nature of startups to overpromise and underdeliver (as that's a common tactic to help raise money), his skepticism seems reasonable to me. I see just as many criticisms of software businesses on this site (actually many more, since there are far more articles about software companies here than hardware companies).
I have very little aerospace experience so I do not claim to be an expert, and while like to see people tackling big problems eventually succeed, his points seem salient to me.