Just thought I would compile a list of possible Air Balloon users and explain their usefulness/how they would affect the metagame.
Only Tyranitar set I can really see using this is DD, but even then, I can't see it being that useful. Basically every EQ user has a way of dealing with it. It can't set up on Hippo without giving it free recovery or getting phazed out, Gliscor can taunt it with ease, Scarf Flygon can switch out and deal with it at a later time and Swampert can phaze. Only thing this is setting up on is CB Dugtrio which is extremely uncommon, and if it's not Choice Band, it can Stone Edge-EQ combo for the kill. TTar would be a bad Balloon user.
Heatran would probably be the most common Balloon user. Balloon would also make it run Hidden Power a lot more than Will-O/Explosion, as mentioned before. This would be to not lose Heatran ditto wars. Overall, this would be a pretty good item for Tran and would function a lot like it does in later gens. The increase in use of Hidden Power might make it a bit more unpredictable. One would have to scout whether it's Grass or Ice (or even Electric oo).
Honestly, I think Lucario would be a really good user of this item. We all know how risky it can be giving this thing free set up, and when you make one of it's weaknesses an immunity, it makes it that much harder to avoid set-up. I think a lot of things would be forced to run certain coverage moves (ie Superpower on Scarftar... EQ's usage would be limited).
Basically, read above. Empoleon would be another fantastic user of this item. Empoleon and Lucario are such fearsome sweepers thanks to their amazing typings and ability to set up.. If you take away one of their few weaknesses (a common type at that) and make it an immunity, they are that much more deadly.
This thing would really just be a better check to stuff like DDTar and Superrachi. I can see Flash Cannon being used over Explosion a lot more on Balloon variants just for the opportunity to touch TTar before it breaks your balloon. Another scenario I can see playing out is coming in on a Scarf Flygon and then just Tbolting any non-ground that wants to come in, getting off big damage. I can see HP Grass rising in usage on this thing too, since you can now come in on Swampert with relative ease.
Anyways, that's all I got. Probably spent too much time on this, but I'm a big fan of theorymonning n_n

Only Tyranitar set I can really see using this is DD, but even then, I can't see it being that useful. Basically every EQ user has a way of dealing with it. It can't set up on Hippo without giving it free recovery or getting phazed out, Gliscor can taunt it with ease, Scarf Flygon can switch out and deal with it at a later time and Swampert can phaze. Only thing this is setting up on is CB Dugtrio which is extremely uncommon, and if it's not Choice Band, it can Stone Edge-EQ combo for the kill. TTar would be a bad Balloon user.

Heatran would probably be the most common Balloon user. Balloon would also make it run Hidden Power a lot more than Will-O/Explosion, as mentioned before. This would be to not lose Heatran ditto wars. Overall, this would be a pretty good item for Tran and would function a lot like it does in later gens. The increase in use of Hidden Power might make it a bit more unpredictable. One would have to scout whether it's Grass or Ice (or even Electric oo).

Honestly, I think Lucario would be a really good user of this item. We all know how risky it can be giving this thing free set up, and when you make one of it's weaknesses an immunity, it makes it that much harder to avoid set-up. I think a lot of things would be forced to run certain coverage moves (ie Superpower on Scarftar... EQ's usage would be limited).

Basically, read above. Empoleon would be another fantastic user of this item. Empoleon and Lucario are such fearsome sweepers thanks to their amazing typings and ability to set up.. If you take away one of their few weaknesses (a common type at that) and make it an immunity, they are that much more deadly.

This thing would really just be a better check to stuff like DDTar and Superrachi. I can see Flash Cannon being used over Explosion a lot more on Balloon variants just for the opportunity to touch TTar before it breaks your balloon. Another scenario I can see playing out is coming in on a Scarf Flygon and then just Tbolting any non-ground that wants to come in, getting off big damage. I can see HP Grass rising in usage on this thing too, since you can now come in on Swampert with relative ease.
Anyways, that's all I got. Probably spent too much time on this, but I'm a big fan of theorymonning n_n