I don't think the wealth of options previously mentioned for "active combat" systems would work well if flight is controlled at the same time – that would be too many keys to press simultaneously. However, that also depends on how flying opponents fight. One can think of a rather stationary battle where the opponents more or less hover, move only slightly back and forth (as well as up and down) or circle each other while almost continually attacking each other – comparable to the ground combat of opponents on foot. There could also be a battle comparable to the fight of knights with lances on horseback: They charge at each other (or one of them at the other one), only trying to hit when they are close to each other ... and maybe using ranged weapons the rest of the time.
For type A fights, combat controls might not need to be changed much compared to previous suggestions, as there isn't much movement necessary while the fight goes on. At least for type B fights, I'd like to have some auto-assistance, I guess. I'd prefer the controls for flying to be simple and not too much like a flight simulator. Any man-sized or larger creature that can fly in a fantasy world would probably need some magical assistance to do so, thus I wouldn't mind if flight were different from what it is for birds/planes/whatever in the real world.
I can also imagine leaving the flying to the computer during a fight, especially if the player character is just the rider. You could give some general rules on what your steed should do, much like you'd set actions for your companions on the ground. A click on the ground or on an enemy would be enough to override those general rules and bring you there (without changing height) or make your steed follow the selected enemy. It's like shouting commands to your steed: It follows them, but they aren't precise enough to make you feel like you'd fly on your own.
Fully controlling how your steed moves would be an option, however. In most RPGs you have full control of the horse you ride, so if it's possible to ride a flying creature, I see no reason why one shouldn't be able to control it as if it was one's own character – as long as this can be done in a simple way.
Another thing that crossed my mind: If we get to play a dragon, weight might play an important part in speed considerations. A dragon should quickly gain momentum when diving, while going up might be a way to quickly lose speed. Of course, that's based on the assumption that dragon flight also relies on the dragon wings and isn't purely magical.
Melee combat against many enemies at the same time, by the way, should be much more dangerous than if you fight them one at a time – and one should also gain more experience from it. The picture of someone cutting through a host of enemies while hardly getting hit is quite heroic, but not very believable. If you assume that you don't get hit because you deflect your enemies' blows with your own weapon, you should only be able to defend against a limited number of foes at a time, probably based on your fighting prowess. A typical mage might only be able to use his staff against one enemy's attacks, a skilled fighter would perhaps be able to deflect the weapons of three enemies – unless magically hasted. All other enemies in close combat range should get a considerable bonus on their attacks. Of course, a hit wouldn't necessarily cause damage if your opponents can't penetrate your diamond armour, but they might still be able to send you to the ground, making it easier again to hit you or to use some nasty special attack on you.
Something I'd also really like to see in combat is intelligent foes who know how to use the available tactical options, however they may look like, to their advantage. In my eyes, it's better to have a smaller arsenal of skills and spells which the AI can handle than a larger range of abilities most of which are never used by any computer-controlled creature or character – or if so, only in a random or stupid manner.
If the player character becomes famous, intelligent enemies might develop countermeasures to tactics he/she is known to use often. They might focus on his/her vulnerabilities if they are able to discover any; differing enemy behaviour would also increase the replayability. They should take cover when being attacked from the sky without having ranged weapons. And many should try to flee if they realize they don't stand a chance against the player character. Most living beings aren't very fond of the prospect to die at the hands of someone who has just easily killed several of their comrades. Simple undead would be a notable exception; orcs and some human fighters might be if they believe that defeat equals dishonour, but death in battle is honourable. And since we just touched it: The various races and factions of the game should be deeply embedded in a rich background of cultural traditions and philosophies.
