I've been thinking long and hard about how magic could play a larger role in Minecraft without ruining the feel or mechanics, and I believe I've come up with a way.
Spell Tables. Allow me to elaborate;
Creating spells would work near identically to how enchanting works. You craft a special table, go to it with a book, and spend X number of XP levels to get a spell, and the spells you get are dictated by how much XP you put into it.
As for the spells themselves, rather than all these extreme things you see in mods or even addons, they could be literally just be potion effects in a new way.
Spell mechanics would work similarly to how using a bow works. You have to click and hold to charge the book, and then release when fully charged. Books would then have a cooldown period before they can be cast again, similar to ender pearls, to prevent spam casting.
The ways a spell would differ from just using potions would be how their effect is given, for example
Beams - The spell travels in the direction the player is facing until it either hits a target, block, or reaches it's distance limit (eg. 10 blocks)
Example of naming: Spell of Healing Beam
Cloud - Similar to how Lingeeing potions work, except it lasts much less time. The spell creates a cloud around the player in a spherical shape, excluding where walls block the line of sight, likely in a range of a mere 3-5 blocks around the player casting the spell.
Example name: Spell of Poison Cloud
Explosive - This spell type is more of a long range thrown spell than a beam. A colored ball could be thrown from the player with mechanics similar to snowballs, but with a smaller range. Upon impact, the spell explodes in a spherical manner effecting any players or mobs in it's cloud. Thrown range could be around 10 blocks, while explosion radius would only be 3 blocks.
Example name: Spell of Explosive Harming
Spell books could either use XP as a sort of mana, making them have to be used more sparingly, or have an incredibly low durability making them break after, say, 20 uses.
The spells could also be used as a way to finally introduce Blindness and Nausea to vanilla play without mods, addons, or commands, finally bringing them out of the unused features list.
I already know something like this is incredibly unlikely to be added, but it's an idea to introduce such an idea without ruining the feel of mc too badly