I searched the forums to see if this had been suggested and as far as I can tell, the only bridge suggested have been water bridges. But what about rope bridges... for the mountainous areas. Usually, those plateaus are too small to live on individually, but if you could connect them with rope briges (two rope and the number of boards would vary depending on length) that would be awesome. Be like Thunderbluff from wow This would also provide a different means of "defense". I haven't thoroughly explored the mountain regions b/c I've only just gotten the skills and humours to do so.
But, this would be fun to implement I believe.