I would like, in addition to existing magic systems, for D&D to offer:
Harry Potter. Yes, you can kill someone at will. Yes, you can levitate at will. Yes, you can teleport at will. Out of character you probably have some sort of mana meter that wears out if you use magic too much too quickly. Also, you can deflect incoming spells (perhaps represented as giving you a bonus to your defenses or saves).
X-Men. You don't have to be a wizard who knows a dozen different spells. You can be a character with just one magic power. I really don't think any D&D edition has done a good job of this. If I just want someone who can fly but otherwise can't use magic, I'm out of luck. (In 4e you could kinda do it by multiclassing into a spellcasting class and taking a utility power, but then you'd just be flying for a very limited duration.)
Magic: the Gathering. You start out combat with limited magical power, but slowly you gather the mana necessary to pull off amazing things. You have a limited suite of spells available to you at a given moment, but narratively you seem to be encouraged to adventure and explore so you can gain access to new spells. It's similar to D&D -- 60 cards might be analogous to preparing 60 spells from your spellbook -- but Magic ends up with a much more epic-level scope. A duel of two planeswalkers usually involves multiple summoned creatures active at a time and clever use of resources instead of just blasting away.