What I'd like to see...? Careful what you ask for...
What I'd like to see is a magical continuum of themed Magic Circles... A framework for writing magical mods, as an Open Mod that would encourage and facilitate content contribution from other coders and from non-coders/users.
It would facilitate a broad range of magical circles too large to be written by any one coder and would require an army of contributors for content.
Not so much a content mod in itself, but a common API framework with classes drawing from editable configs, an asset library for sounds and graphics, and contextual keymapping.
It would be designed around child mods being added with each child mod (Magic Circle) having a theme... Arthurian, Norse, Babylonian, Lovecraftian... etc
It would allow for
Items
potions (selectable single use spell container with slots for spells)
scrolls (selectable multi-use spell container with slots for spells)
armor (worn item with spell slots)
weapons (selected hotbar item with spell slots which can be individually configured either for additional melee effect or for hotkeyed casting for the armed weapon)
baubles (inventory item with slots)
utility belts / spell books (hotbar item with keymapped slots independent of the item being in hand)
crafting components (an ore dictionary-like registry for ingredient/recipe items)
Spells
Assets (graphics and sound files)
possibly Races, Classes, Mobs and Bosses
So far as I can determine Blocks would still have to be added in the creation of the child mod, but I could be wrong about that.
A spell for example, in this mod would be defined in a formatted text file and might look something like
Magic Circle Name - <>
Contributor <optional>
Spell Name - <>
Spell Type - < attack | defense | buff/poison | utility >
{
attack type <(damage on armor / ignore armor) | (damage against magic resistance / ignore magic resistance)
defense < as armor | as damage reduction | as magic resistance | as damage reflection | as damaging armor>
Magnitude - <valrange>
Duration - <valrange or null>
buff/poison < buff | poison>
Magnitude - <valrange>
Duration - <valrange or null>
Effect - < damage(valrange) | nerf regen(valrange) | damage on mana(valrange) | nerf mana regen(valrange) | hunger(valrange) | steal health(valrange) | steal mana(valrange)...
Target - < self | player | mob | block | area ...>
etc...
Because everything added would be obedient to the same rules, Magic Circles could overlap and interact in predictable ways.
It would amount to a template system in which non-coders could contribute major portions of the content.
I can think of a dozen magic circles that could be added and I would just jump on the chance to port content from my text MUDs into a 3D Minecraft world.
A flat file would no doubt slow things down a bit, but on running, the mod could save new additions or changes in the flat files as pre-formatted classes.
It would then only check the flat files for changes on loading and then skip that part when possible.
If someone builds this... the army of content writers will be forming up ranks before the last line of code is compiled.