The only problem with Magisk (and rooting in general, comes from android.gadgethacks - "Going forward, you'll have to avoid root apps that modify your system partition in any way." So if you want to modify any system file - say, to allow pre-Lollipop access to the SD card, you have to wait for someone to figure out a way to modify a system file "without modifying a system file".
It's like evolution. Developers develop hacks to get around defenses, Google builds better defenses to get around the hacks. Oreo might just have an API to detect Magisk, and you're back to where we were before, until someone comes up with something new. (Or until Google realizes that some of us just don't want to run Linux without superuser access. Just modify the warranties to not cover damage caused by access to system files.)