For my campaign I have decided to no narrow my magical system into one set of rules or ideas. Instead I have done the opposite. We don’t know all science and how it interacts and so I am trying to create a magic "system" which relies on several dozen different magic systems which can be used separately to achieve similar ends.
Moreover I want to have these systems be able to work together in open ended ways, with the results being more predictable the closer the two systems are.
For example, the art of enchantment relies on binding magical forces to items in set routines. Runic magic relies on an ancient language of written words of power. The two systems are dissimilar but both require a lot of work and are usually used to create enchantments and so share some similarities. Thus, the interaction of the two could create somewhat predictable results. An enchanted sword of flame, inscribed with a rune for cold could thus burn and emit cold, cracking rock (or perhaps itself). Or the result could be a sword, which emits cold fire. Or perhaps one that does extra fire damage to creatures of cold etc. By combining systems could range from predictable to wildly unpredictable.
So my request and challenge to everyone is for different magic systems (means to ends, not ends) and how the various systems could theoretically interact with other systems.