Sounds like it has merit, but I think it's already covered (at least everything that's been mentioned in this thread). What isn't covered is apparent the need to be able to specify rather a unit's model rotates with the ground's slope or not. It wouldn't make sense for two-legged humans to lean to one side when standing on a hill, but it would for a 4-wheeled catapult or an 8 legged spider!
So back to your idea, I think this will actually be covered (up to 90 degrees) with the min/max incline functionality I've proposed for 0.3. I have also proposed multiple move skills, primarily to manage swimming. However, it can also be used to specify a different move skills that apply to different inclines/declines and you can add your suction-cup sounds there. All of this is planned for 0.3 already.