The nether right now is kinda boring. Just open fiery land and a few fortresses. I think it could be made more interesting by adding a few more structures similarly to dungeons, mineshafts, and other overworld stuff. If generated strutures were turned off these would not generate.
1. Nether Spires
Remember the Nether Reactor from the Pocket Edition? And how it spawns a huge tower? I was thinking about having similar towers spawn rars! ely in the nether. They would be made of netherbrick instead of netherrack, and they wouldn't decay- instead, they would be solid towers with multiple floors. Also, Zombie Pigman Spawners would be hidden in cases of obsidian- similarly to how the nether reactor core is encased in obsidian, except there are multiple per tower. Also, random chests would spawn with loot similar to fortresses.
Basically, bridges over Lava Lakes, or other gaps. Not really much else to it.
Feel free to suggest more types of buildings! What do you think?