I think the sad reality is that if more models used were sizes 6/8/10 all you'd get is debate over whether they are actually a "healthy weight" from the thin police. Or fight from the body posi crowd that they aren't a good representation for x petty reason, y petty reason, and z petty reason. I'd hope eventually things would even out as having more medium sized models was embraced again, but it'd be a pain in the ass for a while.
Well, that and designers would be forced to make clothes for actual women's bodies, instead of expecting models to be walking coat hangers.
A good example of the damned-if-you-do, damned-if-you-don't aspect of fashion would be the way people treat Crystal Renn. Too skinny to be plus-sized, too "fat" to be a straight-sized model. At her smallest she was a 0, which is extremely unhealthy for someone who's 5'9", and at her biggest she was a size 16. Nowadays, according to her, depending on the designer she'll wear anything from a 6 to a 10.
A few years ago she lost some weight, and people were screeching about it on the internet because in an interview she said she wasn't really trying to lose weight. The part they ignored was, she mentioned that she was eating right and exercising. It just so happened that her lifestyle change caused her to lose weight.
Plus-size Crystal:
Crystal... recently? This campaign was from early-ish 2016:
Personally I think, as long as she's taking care of herself and she'd happy, let the woman do what she wants. I've read her book, I know about all the shit she went through with her eating disorder when she was a straight-sized model, and I'm glad she's healthy.
Also, I'd snap someone's neck like a Navy SEAL if it meant I could wake up tomorrow looking like her...
I'm sure there are other examples, this is just the one I've been most aware of.