Will what you have in mind be completely different from fashion and beauty?
Fashion and beauty are such a huge niche that can be split into many smaller niches ie face masks or swimsuits for pregnant women and sending emails about baby coats or acupuncture may be seen as connected to what they originally expected to receive from you to some but not all of your subscribers.
As fashion and beauty is a huge niche, I think you could 'get away' with many connections to beauty and fashion in your emails though. For example fashion book recommendations, courses in beauty, documentary beauty films Even flight recommendations! Where else is the best place to get really pampered and relaxed than a spa abroad in a sunny climate?
Only your current subscribers can truly answer this one me thinks as they will either vote a yes by still opening and clicking your email links or they'll vote a no with an unsubscribe click.
Have you thought of creating another email list in the completely different niches you're thinking about or segmenting (dividing list into interested or not) your current list with a survey? This way you'll end up with interested subscribers who at least will continue to open your emails.