I think a good solution would be to have opinion pieces in another subdomain such as blogs.mynewspaper.com/ephraimgoldstein with a very different design from the rest of the paper.
Like the way editorials in print newspapers are always left justified (ragged right), while news articles are fully justified[0]. It's subtle, but for anyone who's been reading newspapers regularly, it's immediately obvious.
The problem, if there exists one at all, is the reader ignoring words on the page of a publication that is expressly about transmitting words.
That said, the Guardian already uses a completely different highlight colour for its Opinion section than it uses for its News section.