We just did a shower in a bathroom with 9' ceilings and had the same dilemma. We ended up tiling to the ceiling and doing glass doors on 2 sides about 7' high. Looks great. I thought it might look odd having the tile stop before the ceiling. Also water droplets would sit on the little ledge at the top of the tile where it met the drywall and could be a cause for leakage. We felt it safer to have tile all the way to the top. Hope that makes some sense?

Anything goes as long as you tile above 7'6". Shower neck (comes out of the wall and is attached to the shower head?) is code required to be at 7'0". We will typically go all the way for 8' ceilings and rarely do lower...but most pre-fab enclosures are sized to fit below the 8' ceiling for easier installation.