You left out an important detail: the grappler can move you at half speed. I wouldn't find that very conducive to flying (unless the two-sizes smaller rule comes into effect).
Prone's not a penalty. But sure, if you're lying on the ground and someone grabs your scruff and drags you along, you'll probably still be there when she lets go.
I saw nothing in the rules about "dangling" feet. Speed is zero because that character is not allowed to move on his turn. Interestingly, since dropping prone doesn't require speed, a standing, grappled character can go prone while being grappled. Also interestingly, a grappled character can grapple the grappler (a flying creature, perhaps?), and cause the grappler's speed to be zero if successful.
"Being Prone: combatants often find themselves lying on the ground." I'd say removal from the ground counts as ending prone.
Again, flying at half speed sounds dangerous. Getting grappled while flying: even more dangerous. But sure, magical flight doesn't care about that. Unless the grappled grapples you while flying: then it makes no sense for your speed to become zero.
Winner: rulings, not rules.
Ok i left half speed out but it is still moving contrary to your comment.
Moving at half speed typically (not always) gets them 15ft away, out of melee if flying up.
Dangerous it can be, but I don't see flying becoming non conducive (possible/likely) because of this. And the are many situations where it could be a good option, say around clifts.
Dangerous =/= conducive to play. It may be unwise, silly, and yes dangerous, but it may be the best option given the circumstances. It alo may be less dangerous for a strong flyer facing a melee focused group to remover someone this way.
Sure 'dangling feet' are not in the grapple rules, but neither is 'made prone'. Prone is a separate condition. I feel a bear hug a better image conceptionally and more conducive to the flow of play then being prone, because
1- bear hug you only push away what is holding you, land on your feet (not far enough to be called a fall).
2-made prone, and breaking away you are either prone, with all that entails, or get a no move cost stand.
And prone may be an issue. If you don't like penalties then problem (advantaged melee attacks within 5ft (which can be substituted for a shove or grapple), disadvantaged attacks from prone), and or a bonus (disadvantaged range attacks v prone) or both at once. Then there's the standing up from prone using 1/2 your speed.
If a grappled person went prone? My rulings
If on the ground, would still be grappled because they would still be in reach, but now also prone.
In the air? Since you haven't broken the grapple you are still being held. I don't see it reasonable that
1 it frees you from the grapple, and
2 (based on your earlier comments summed up as prone = on the ground), places you prone on the ground. I consider it one of those times it is outside the 'often on the ground' part of prone. Breaking the grapple and falling probably leaves you prone. Again my ruling would be if prone pre-grapple the then you are prone after hitting the ground and. If standing pre-grapple stay standing. Then for both follow the falling rules (which depending on the drop distance and your interpretation of immune may mean still standing if standing pre-grapple)
Just to be sure though, you state removal from ground = no longer prone and grappled = on the ground. What if already off the ground when grappled? Because until this reply, removal from ground = not prone and flying has you removed from the ground
I do prefer that the one grappled can't do anything other then try to escape the grapple, as that would limit the counter grapple. But that gets into house rules.
