I know the battle system is getting re-tuned, as well as the magic system. Right now magic oriented sovereigns are weak compared to warrior tech'ed sovereigns. Stacks of well armored and well armed units will easily crush a sovereign who has neglected the warfare tech so that they can pursue the magic tech. At least in the end game.
What Id like to suggest is, in addition to more spell diversity, is more unit diversity for summoning mages, and having it tied to the shards they decide to harvest. More than just the elemental types in the game right now. So for example lets say a sovereign starts out in a game and he sees that immediately in his area there happens to be an air shard. So he decides to take advantage of that and techs up in magic and goes up the air magic tech and/or summoning. To compete with a warrior tech sovereign who has stacks of knights and archers, he could summon say air units for that specific shard. For example, flying units, units that have a push back air attack, stealthed units, lightning wielding units, etc. The more shards of that element, the more powerful unit the mage would be able to summon or create.
In addition, each elemental unit type could have a counter. So for example the flying units could be rooted by earth magic or some of its units, or even spiders with their web ability for some non-elemental unit types, archers, etc.. Fire would be vulnerable to water/ice elemental spells/units, and so on
Maybe some of the most powerful and mythical units equivalent to a company of mounted knights would require several different shard types (ie., a dragon for example might need at least one shard of each type to summon)
Not only would this make tactical combat more lively and fun, it would allow mages a little more leg up, as magic is weak right now and unless massive area of effect spells of doom are implemented, cant compete with stacks of heavy armored, well armed high attack units.
Mage sovereign's units would become more elemental and could compete with warrior sovereigns. Perhaps there could be a trade off between having more powerful elemental unit diversity vs more powerful elemental spells.