see now, I thought you were going to say it was.   So I came running thinking "THEY DO!?" but now I see its a suggestion.    yeah, totally.   Light of sight should totally be effected by mountains and trees.   Problem is that tall mountains should be able to be seen over short mountains and that sort of thing.  Lots of complex stuff that could exist there.

Hight should be a factor, so mountains can be seen over tree tiles (with reason)  and trees perhaps should limit line of sight to only 1 space (wich exceptions)

From the PAX pics, it seems they might have a bit more terrain detail in the non-cloth map version so hopefully some of that complexity is already there and it'd just be a matter of coding some standard LOS rules. 

Good feature?

To me, it sounds about as necessary as gravity pointing down in-game. Plus it would allow for using cover to mask your armies approach.

Seems like something that should be implemented to me as well...

I like that, and you could extend that to dragon or other flying units having no sight penalty for mountains or such.  Or increased visability range like a scout would have.