I, for one, don't want scalable mountains. Mountains should represent stark, impenatrable natural barriers - not something that can be hopped over with a horse and enough patience. Players should be forced to explore underground caverns and rugged mountain passes to traverse this hostile terrain.

In Oblivion, I was annoyed to no end at the inconsistency of mountain climbing. Some you could hop up, some you couldn't...but they'd be the same height and grade, which made no sense. I'd like to see surpassable mountains look the part, with insurpassable mountains looking high and treacherous - basically saying to the player "don't even try it".

One uses climbing /ice axes to climb mountains, pick axes are for mining, and damn heavy.
Climbing axes are smaller, lighter, and fit into loops on many internal frame packs. They'd also probably hurt if one were hit with them.
But a climbing skill would be awesome, as well as including climbing /ice axes in Skyrim. Avalanches would be pretty cool too.

Impossible? No. Brutal difficulty? Yes. There should always be those spots that are unimaginably difficult to get too, else the Himalayas would be just another mound of Earth with no real significance in reaching the top. I want to have a real movement and travelling challenge, a spot where I'll be forced to use a combination of skills, magic and quick keyboard-work to get there, kind of like the ultimate challenge.

Of course I'm not talking something as simple as find the right path up the diagonal mountain, no my friends, I'm talking going through the mountain form one side to the other through uneven cave-systems, using telekinesis to form an artificial bridge, blowing up some rocks blocking your path with a fireball spell, days of trekking, etc. This is by far no simple challenge, there is no chance that I would want it to be anything of the sort.

This, it would give more reason to explore and would a fun challenge imo.

I think the really tall mountains in Skyrim should be situated at the top or border of the map. These mountains would be unclimbable (doubt they will add a climbing skill), but they should have hidden footpaths or passageways or something that could still lead you to some of the summits. You should also be able to go anywhere with levitation. The rest of the mountains in the province could be smaller, more scalable types like in Oblivion.