This is surely going to be optional, so it won't impact me in the slightest, but it is a pet peeve of mine when browsers (or browser extensions, looking at you 1Password) alter the UI of websites away from how they were originally designed without explicit instruction to do so.

This sounds like it meets that threshold, it will just surely be a hit-or-miss mess. Hopefully if it makes it to iOS it will drive more site owners to adapt to `prefers-color-scheme`.