Maybe ascending Mons Olympus?

That was my initial idea. Its the tallest mountain in the solar system so it'd be a no brainer to have a raid here. Except I thought "why wouldn't your ship just fly up and drop you off at the top?" Only until later when I wrote this I realized there are ways around that like a scrambler or EMP radius. Its not unlikely since the Cabal are militaristic anyway, so some kind of EMP that prevents you from flying up wouldn't be unbelievable.

Maybe it would be littered with thousands anti-air weapons? Or maybe you could take a vex portal hijacked by the cabal which would take you to the entrance to a cabal stronghold miles under the mountain, and for the final battle, you ride a lava plume something like 20 miles upward from deep underground to the top of the mountain in a matter of just a few minutes. You could follow the boss up there using a sort of lava-using elevator. The boss, however wouldn't be in the elevator and would be in instead be in his vehicle, which would be a sort of high-speed, heavily-armored, hybrid of an interceptor tank and a goliath tank. You and your fire team would then chase after him down the mountain on sparrows, and you'd have a ten minute time limit to take him out before he escapes over a cliff and joins the rest of his army. You'd be able to shoot him on you sparrows (first person only for sparrow riding), throw grenades, if you get close enough and don't die, maybe even melee, use supers (they'd be modified for the situation. Example: Arc blades would throw blades, fist of havoc would have extended range and would simply be the titan punching the ground on his sparrow, ward of dawn would be larger and stay with the player, and all other supers would stay the same but all would be in first-person perspective). Also, turrets, troops, interceptor tanks and goliath tanks, other vehicles, various types of air-ships, and more would all be firing at you. You could change the bosses route by cutting him off and other ways.

You're well on your way to creating your own raid :)

This is true! I heard Titan, one of Saturn's moons has tall mountains. [spoiler]Maybe in my next raid :)[/spoiler]