...who would buy airplanes, increasing their customer base.
I know what you mean, but, just to nitpick, most small airlines will lease the planes
From people who bought the airplanes...
Yes, of course, the theory is clear. I still can't help suspecting that this whole "Startup" organization is a boondoggle so somebody's brother-in-law can be a VP in charge of something harmless. At Boeing's scale, purchases (or leases) of new (or at least new enough to affect demand for new) planes by investors who can't hire their own experienced airline executives will necessarily be a drop in the bucket.
Experienced airline executives often use outside consultants for specific areas of expertise, and national governments have a fondness for starting airlines and purchasing multiple new aircraft. It's probably the only marketing division of Boeing that turns a profit :)
Even an airplane that is leased is built on specs by the "end-user"; analogue to a house which owned by the bank (by mortgage).
Yes, and in giving this advice they are forming a positive association between the entrepreneur and Boeing.