As I see it, 6th Edition has two major flaws to its implementation of flyers.
1) All flyers can utilize Skyfire.
This is the big one. It gives flyers with hover mode a distinct maneuverability advantage over dedicated interceptors, while not impeding their firepower. It makes heavily armored gunships and transports like the Vendetta a deadly threat to supersonic fighters. Logically, slower and heavier ships with heavy ground-targeting firepower should be more vulnerable to fighters, but this isn't the case.
2) The Interceptor rule ties air/ground firepower to reserves interception.
This constricts the options for future weapons by making it impossible to have a versatile weapon that isn't also an AA interception system.
To fix this I've come up with two new special rules and a few pieces of errata.
New Special Rules
Some flyers act in a dedicated ground-attack or transport role. While still capable of fast, high-altitude flight, these heavier ships are slower and more vulnerable to air attack.
Flyers with the Gunship special rule may not choose to use Skyfire, unless they have weapons that specifically permit them to do so.
These weapons utilize advanced technology to guide their fire. They are as agile and dangerous to those in flight as they are to those on the ground.
Weapons with the Targeting Spirits special rule may choose whether or not to use the Skyfire special rule at the start of each Shooting phase.
Valkyrie: Add the Gunship special rule.
Vendetta: Add the Gunship special rule.
Vulture: Add the Gunship special rule.
Hellstrike Missile: Add the Targeting Spirits special rule.
That takes care of the more egregious offenders. I think cases could be made for the Storm Raven/Eagle, the ork Blitza or Burna Bommas, the new Avenger, and several of the Forge World super-heavy flyers as well. I'm not as familiar with the rules for them, however, and am disinclined to list every single combination. I figure common sense can generally be used here:
If a flyer is not a fighter, it's a gunship.
If a gunship is equipped with air-defense weapons, those weapons have Skyfire. If they can be used as either air defense or ground attack, they have Targeting Spirits.
Let me know what you think.