I have an MIT-licensed library that supports user-provided backends. I was asked to implement a backend that would require using a GPL-licensed library. If I write such a backend, license it's files as GPL, and have no dependence from my MIT code on the GPL code (the user would have to load and enable the GPL-backed), would that be acceptable under the terms of the GPL?
This questions indicates that it'd be allowed if I put them in separate repositories. So, would it be a "mere aggregation" if I put all of the files in the same repository?
If it makes a difference, the user would have to specifically load the file, then set a global variable in the main library to an interface function from the GPL-licensed code.