commonly used implies possible and feasible. I note that "when" appears in both phrases.
Precisely; "common use" predicates possibility and feasibility, and so is asking "when will X be commonly used?" is a stronger question that "when will X be possible or feasible?".
Showcase prototypes don't really count in any practical sense as "have the technology."
They do if you draw a distinction between possibility and feasibility.
Also, to claim that flying vehicles imply "much better transportation systems" is gratuitous. How would they be better?
See previous posts.
The statistics could be calculated from any old census (and school) data.
Well, that's just it -- this is an improvement on the collection method. I'm not suggesting schools have fingerprint readers at schools, I'm merely stating that this method will likely produce more accurate census data, which could then be used for any of the reasons mentioned.
The easiest way to figure the cost of living is to take your income and add ten percent.