Managing and switching spells breaks action RPGs. A melee character can quick strike, power strike, lunge and knock back while never changing to another weapon. Much more satisfying and engaging. I believe magic can feel more visceral and dynamic. Here is an example.
Fireball
1. Quick taps let loose mini fire balls
2. Holding the button down charges a fireball (basic fireball->AoE fireball->Exploding AoE fireball) release when desired.
3. quick tap followed by a tap and hold creates cone of fire.
Shift or trigger+fireball key
4. Press once to lay a glyph
5. Hold to create walls of fire along where your target is focused on.
Seven fire spells with the same icon/quick key. Mana cost would very with each spell version and spells would be affected by talents and stats. This can be done with other spells like the summoning spell.
Summon Skeleton
1. Press once for basic skeleton
2. Charge for improve more powerful version
3. Tap and then hold summon multiple weaker versions
Shift or trigger + summon
4. Lay a glyph that when triggers summons a skeleton on spot.
5. Hold to create a more powerful skeleton glyph
This would make play control of mage classes so much more enjoyable. With six hot keys you could have 30 some odd spells at your figure tips.