My two cents there:
Yes, its a publicity stunt. But a pretty good one to showcase what is possible with photovoltaics if you want to. Its sure in no way what the future of air travel will be like. But who knows what kind of job photovoltaics could play in air travel - if light enough, you could produce additional power for the already very electric airliners, which could save a few tons of jet fuel.
Maybe the developments in electric cars will result in viable electric airliners one day. The problem of replacing gasoline with electricity is actually something interesting for airliners, since jet engines have way less efficiency than car engines, so an all electric plane could really become simpler than an all electric car.
And no, speed does not really matter that much for air travel. If you would make it cheap enough, people would also fly from Europe to the USA in 16 hours. Think of a ground effect vehicle there - such a vehicle could get from Europe to the USA in about 24 hours (at 400 km/h), but would require much less fuel per passenger (or passenger comfort)