hmmm I just thought of spell, I'd love to see more spells that take the elemental shards into affect. Like spells that affect tactical battles but you cast them before hand before going into battle. Like how you cast the spell that gives life to the land if your Kingdom and thus gain a bonus or if you cast the Desolate spell which favors Empire.
Idea here is to make use of the elemental shards you have in possession, a lot of them I've seen don't have many pre-battle affections.
Example: if you have a Water Shard, you gain use of a spell called Torrential Downpour and can affect yes both armies on the field. How many armies have lost or won a battle due to weather? LOTS, far too many to count, the Torrential Downpour could affect a certain number of squares on the field, whether they be your lands, neutral lands or enemy lands. You see an army with siege engines heading towards your territory and want to plan ahead for the attack, so you cast this spell, what it does then is slow the enemy down and also makes them incur a defense penalty because they are bogged down by the rainy and muddy terrain.
It's just an idea but I think it would bring even more tactics into the game if such spells were implemented more.