An airship doesn't need armor (Armoring the gondulas maybe). And weapons/crew weight aren't really a problem either. They got very good cargo capacity (Better cost/cargo ratio than aircraft anyway). Besides, it's not like there's a size limit or something.
Also, the 10,000 meters was a good guess on what our current designs might accomplish when equipped with the technology. Specially designed ships could get higher, and well, shooting things down that are moving upward is fairly easy.
It feels to me that aeroplanes have hit a bit of a wall. The engines are improving, but also getting heavier, the actual power to weight ratios have been fairly static and all that we are doing right now is filling different roles and swapping around armaments. The next likely revolution would be rocket-propelled aeroplanes and our enemies have shown no interest in rockets. The only really scary thing they could pull out quickly is armoured wings, which will hardly make for an effective fighter against other aeroplanes...
Or you know, jet engines. Besides, rocket propelled airplanes have several large flaws. Tendency to explode, very high speeds knocking people out, hard to manoever, high minimum speed, eats away at fuel, impossible to land.
Meanwhile, the lack of advancement in airships is largely a matter of interest in the field. We could experiment with rigid frames, lighter gasses, spare gas tanks... My next idea for a repair system is a miniature airship, able to support a single person, with tethered clips to navigate around the outside of the major airship, a bit like space-walking... If you really want to invest in the future, go for rocket-powered aeroplanes, they can intercept effectively in a few minutes, fire devastating volleys, and sometime land afterwards!
Rigid frames don't really offer much benefits. Sure, they are more stable, and allow for larger craft sizes, but they're also more complicated.
Lighter gasses is impossible. Hydrogen is the lightest molecule available, with helium soon after. ((Sure, you could try heating it up, but that really isn't worth the cost)). We could try to go for vacuum as flotation gasses, but I'm certain you can see the drawbacks. Hybrid airships could work.
Also, the repair system is slightly unfeasible. Astronauts have severe trouble moving in their suits, image the problems on Earth, with a giant balloon keeping you up, constantly catching the weight. Besides, using single man repair teams is kinda unfeasible when you would be talking about hundreds of holes.
On a side note, a rigid airship might solve the repair problem. Because then you can go and deflate individual ballonets without risking structural integrity failure. Makes it much easier to repair/replace them.
Lets start work on a massive Flying Fortress kind of bomber.
2 14mm MGs in staggered waist positions
2X 14mm MGs nose and tail turrets
2x 14mm MGs in ,dorsal and ventral turrets
4 14mm MGs in wing(under and on top of wings) turrets
6 Improved V12 Aviation Engines
Crew: 11-14
Aim for a Bomb load of 50k kg plus and space for 75+ men
Try to focus on range as well.
Too big and too slow to evade it should just smash its way through any fighters, with its guns killing any thing that enters 2000M.
if we get powered turrets then id bump some of the guns up to 25mm and issue Proximity Shells
That thing has a ludricous payload. In fact, you could load up 2 fully loaded B-17 flying fortress bombers in it's cargo bay.
Besides, it won't work. The B-17 success was due to it's high flight altitude. Your thing is practically AA fodder, as it can't evade not outrange even the most basic of AA systems.
Edit: Funny little calculation
1200kw(engine power)*6/s= 7,2*10
6Joules 7200000
50000 kg*9.81N*h= 4,9*10
5 490500
Meaning that it would need to spend almost 10% of it's engine power just to keep it's payload aloft. Include the plane's weight, it's ammunition and it's fuel that'll probably be more than 20%.