I've read through all of this and seen a few instances of "How about some climbing?" "No wai bucko, this is Elder Scrolls, not Spiderman's Creed!"... So does this mean everybody has forgotten Daggerfall? I'm sure Arena would've had it too if it'd been a little more ambitious and/or technologically advanced.
I actually have an idea for meshing Assassin's Creed-style climbing with a skill-based RPG. When any object (building, rock, tree or whatever) is modelled, the modeller can choose edges or an entire section of the wireframe and edit the climbing properties for that particular "grabby spot". The lower the number you enter, the easier it is to grab.
For instance, imagine you're modelling a house. So you select the edges that make up a windowsill on the second floor. It protrudes quite a bit, so it'll be easy to grab, meaning it should have a rather low number entered into its climbing property box. Now, a little further up the wall there might be a crack in the spackle where a more skilled climber would be able to jam his hand into and get a grip. This place would have a higher value in the climbing properties field.
So the player will only be able to grab a particular feature if he has a climbing skill that is equal to or higher than the feature's climbing property. Furthermore, if your climbing skill is higher than the feature's number, you should traverse it faster, so someone with that skill maxed-out will pretty much fly right past an easy ledge with a value of, say, 12 as if he was Son of Kong or something.
So, if you can get past the idea that climbing has no place in TES (because it totally does- scaling the city walls at night in Daggerfall was pretty rad), do you think that idea is totally ridiculous?