Overall: I would say that powered flight is at the outside edge of feasible on Jupiter. How would you design a aircraft for Jupiter?
1) Dirigible using heated hydrogen for lift. While you could manage buoyancy, the end result would be not usable. Not sure how your floating cities are supposed to work, but even using the unobtanium for lift still has a problem. Landing these may be impossible due to high wind velocity (350 kph being common).
If the cities are allowed to move with the air currents you still have problems controlling flight in the intervening space to avoid being blown off course. Due to the size of Jupiter balloon flight will be very slow to cover significant fractions of the planetary circumference.
2) Airplane. You need a lift / air-frame mass ratio greater then 2.5 to keep aloft and carry cargo. A heavy lift plane C-5 Galaxy has a maximum take-off weight of 769,000 lbs and dry weight of 380,00 pounds a ratio of 2.02 : 1 -- s, A 747-400 is 2.22:1, Airbus A310-300F is also 2.21:1
So, given a little more attention to better materials, etc. a lift ratio over 2.5 is likely feasible (though a bit expensive), not that the net cargo capacity will likely be fairly poor.
You still have a pretty marginal design though. Is there anything you can do? Yes, assist the plane at take and landing just like they do on an aircraft carrier. It may expensive, but it is cheaper than building sky bridges.
What about fuel? For a hydrogen atmosphere, you need to carry an oxidizer. But you have a real problem, the weight is really working against you. Burning hydrocarbons on earth, you carry only a small mass fraction of the end products of combustion. Both C02 and H2O are mostly oxygen by weight, so you get most of the mass from the atmosphere. And on earth a 2.2 lift ratio allows you to carry a lot fuel (perhaps 30 tons or so) and still carry a reasonable amount of cargo. On Jupiter, the physics and chemistry are both working against you pretty hard.
Maybe it is time to make a nuclear air plane. The US air-force wanted some of these in the days before ICBM so that they keep planes in flight for weeks at a time. The nuclear plant that they liked used a molten salt reactor -- no heavy pressure containment vessel, and other advantages made this look at least feasible. A 747 requires about 90 MW for takeoff, about 45 MW for cruising -- this is small compared to a commercial nuclear plant.
Anyway, GE built a small (2.5 MW) molten salt reactor for testing and it was generally considered viable. Unfortunately I could not find any data re: the mass of this experimental reactor. They actually flew the reactor around, though they did not use it to operate the plane.
Also for those keeping their fingers crossed, Lockheed Martin claims to have a small fusion reactor available in a 100 MW prototype by 2025. The only size claim I've seen is mentioned in the article in that it would fit on a truck.
So, I would say that powered flight is at the outside edge of feasible on Jupiter. Larger designs in particular may be feasible as a nuclear plant does not necessarily scale up in a linear manner. Given the large size of Jupiter, airplanes would certainly be very desirable to reduce transportation times.
Finally, some things that would be desirable for flight on Jupiter-- speed of sound would be roughly 3 times that of earth normal atmosphere (at the same temperature) because the molecules are very light, and the viscosity. Hydrogen has less than half the viscosity of air though helium is slightly higher than air, the overall mix should be a little less than half of air. So you get to cruise a lot faster for the same energy consumption.