Ok, now I fully understand. That’s tough man.
Option 2 seems like the best… but it doesn’t answer your question. I see no problem with requesting that people make a few changes to use your plugin. All plugins have some criteria for use. If the end user want to have a non-valid site… well, at least they’ve been warned.
As for option 3… I don’t know. I would assume you could get the styles if they were inline but that’s the worst option ever. Requiring users to have inline styles is much worse than requiring them to use classes.