Think of it this way: In the final battle between Avatar Aang and Fire Lord Ozai, Aang creates this sphere-like compressed air thingy with him inside it. Now is it possible to do this, but instead of compressed air it be a vacuum?
If this is possible, could this be the subset of Airbending?
And if Aang (or any other Airbender) can create vacuums in the air, wouldn't it make sense instead of fighting the Firebenders to just create vacuums around them(since fire needs air (oxygen) to burn)?
Just scenarios that run through my mind sometimes.