Runes of Kilmorph believes in worshipping the earth or some deity/set of philosophies related to the earth which leads to mining and what have you. The Khazad. RoK lore has a lot to do with mines and resources of the earth. The fact that their exists a good synergy between the Khazad and RoK proves nothing. There exists an even better synergy between the Clan and RoK. Does it therefore follow that the Clan should get mountain yields?
Since this argument is about lore, let us look at Khazad (not RoK, it is a completely separate entity) lore. Nowhere in Khazad lore does it state that they mine or work in the mountains. What Khazad lore does make clear is that they have been effectively exiled from the surface for trying to explore it in the first place. Various excerpts go on to depict a Khazad society that is fighting to survive and thrive off of the riches of the surface, not the riches buried deep underground.
I mentioned RoK as both it and the Khazad have the same patron angel, Kilmorph (Earth). I agree that the synergy is irrelevant, though you have to wonder why it's there in the first place.
I doubt your claim about the Khazad lore not mentioning mining/working in the mountains, but I'm reasonably sure it doesn't explicitly say that they don't. The Khazad worldspell gives you gold for every mine in your territory. They like mining.
http://fallfromheaven.wikia.com/wiki/Khazad <-- not sure how accurate this is, but it suggests that they weren't exiled from underground, more that they reached the limits of underground expansion so ventured onto the surface. They also definitely have the expertise necessary to mine mountains.
Ok after chatting some in #erebus here are some additional arguments against it.
A citizen specialists gives +1 hammer. So for it to be actually worth it, the peaks would have to give +2 Hammers, that's the same as an Engineer can give, and they are rare most of the game. (Not counting the GPP). And that sounds like too much to me. (And if you go to 3 it's starting to be too much like a hill)
And they can't be pillaged/blocked by most units. Which is really powerful.
This is a good argument against high constant yield. It doesn't address cottage-like upgrading with a mine (3 ), or bonus hammers from techs.
Even if we let it be constant 2, I'm not sure such an unimproveable tile that doesn't provide GPP is that much of a bonus. It's still not a great tile.
To be useful, you'd want 3+, which is why I liked the 'n turns, get a mine' idea. 'n' can easily be varied so you'd need significant 'citizen' investment to get more production later. This fits with peaks being mostly inaccessible - you'd plunder the foothills first, and then get the resources underneath the mountains after significant effort.
The lack of pillaging/blocking is another factor that can be balanced around, and does not destroy the idea.