I have no idea where you guys are hearing this "preview" for it, but once we get an actual rip I'll see.
As for the q 2 up, It entirely depends on the cover song. If one person is singing in the range of a tenor voice, which is the highest male singing range, and then in the cover song the man is singing in the range of a bass voice, which is the lowest of the male singing range, then they are singing in entirely different octave.... But that doesn't mean the song itself is in a different octave/pitch.
This phenomena occurs when you try to sing a H!P song, but they sing too high-pitched for your voice range, so you drop a full octave and sing with a deep voice so you can sing the song. The pitch/octave of the song is exactly the same! You just are
singing with your own voice in a different octave.
Actually, the perfect example would be today's Green Room when Akari's voice training is happening. When they are singing together, she is singing in a higher octave than him, but they would have used the same instrumental to sing the song. (meaning, their voices are the different pitch, not the song.)
Check the pointless musings thread