Would having the ability to look over terrain if it's below you be a welcomed extension to the map, or not? For example, being able to look down onto the river between the lane and the Ancient Golem (where Urf spawns for the blue team on the Hallowe'en map).

This would be a slightly modified area of sight, providing either more or less sight than you would have if standing on flat terrain (depending on which makes it a fairer mechanic). Perhaps similar to brush, you would be revealed if you attack over a wall? To prevent you just raining death on someone?

I've done a map with all the locations that look like you should be able to see over.

Key:
Blue - Blue Vantage Points
Pink - Pink Vantage Points
Indigo - Questionable Vantage Points (maybe these aren't wanted/affect the game too much?)

Sounds like a bad idea, just having to run back through the safety of your tower if anybody is MIA, would throw off ganks a lot. Maybe through some refining it could work.

It means I play Tristana and drop 3 100% Crit Rate into your face for 300 Gold.

Also this is what wards are for, kinda like how Lee Sin uses them.

Just plop one down during the teamfight = GG.

I love being able to shoot Baron from the ledge.

i like this idea

You wouldn't be able to see into Baron or Dragon, if that's your concern.

I like the general idea, and it would make sense, especially since it was originally a DotA feature. However, because the geometry seems to suggest an upward slope towards the riverbank in the spots you highlight, it would make more sense to only allow vision when immediately above those locations - i.e. you shouldn't be able to see over the ledge unless you're at the ledge. Same goes for the walls - because they're not just cliffs, they're actual walls on top of elevated terrain. But I do agree that if you're at a vantage point, you should have extended vision for the elevation.

I didn't highlight the ramps themselves, only the areas on either side of the ramps.

"...immediately above those locations..."
Assuming I've understood that right, I agree. You should have to be right at the edge to receive the extended vision. Say--if you're hugging the trees--you wouldn't be able to see in the river.

It would be ok if it were reduced vision range, such as during nocturnes ult.

Any amount is better than none I guess.