To balance more powerful spell effects while maintaining a good variety, instead of having spell schools be superior or equal to multiple other skills
(open > security,
shield > or = armor,
invisibility > sneak,
charm > speechcraft, etc.)
make some things require specialization and, if they're going to implement spellmaking, make higher magnitudes and durations require feats. It's possible they're already doing this, I am just bored.

Say we have a base set of spells, let's just make stuff up to simplify since this is all hypothetical and just for some discussion as I know some of you are just sitting around waiting for Skyrim like me -

Conjuration base spells -

Summon Undead I (Ancestral Ghost or similarly weak)
Summon Daedra I (Scamp)
Summon Animal I (Wolf)
Bound Armor I (weaker/lower durability version of daedric items w/out enchants)
Bound Weapon I (as above)
Dismissal I (Unsummons weaker summoned creatures, weaker sends Daedra back to their realms, sends weaker undead back to death, and frightens/weakens/damages mid level of the same types)

This kind of groups up the spell effects into subsets, and with feats you could specialize in specific summon types - being a more necromantic type, druidic, or daedric specialist, gaining stronger vesions of the spell type at higher level in the skill, and the strongest with special feats. Same for stronger bound items, more powerful anti-summons/undead/daedra spells, and so on.

The primary idea is to make spell casters less jack of all trades so mages can't solve all problems easier than those specializing in skills specifically to do what some spells do better, without sacrificing variety of spells - just making specialization required for the powerful stuff so no two mages are alike.

For example some different potential mages -

Conjuration - Animal summon specialization
Destruction - Lightning specialization
Alteration - Travel specialization (water walk/breathing, levitate, etc.)
Restoration - Healing specialization
Naturalist/Druidic sort

Bound item specialization
Ward specialization (Shields)
Fortification specialization (physical stat boosts)
Battlemage sort