I wonder that too. I think the trend right now is micropave/delicate settings/halos. Since I have all of the above (and a double halo!), I hope it's not outdated anytime soon! But my mom, like whoops' mom, is really into giant baguette burst style on rings, and even though she likes my ring, she still thinks that style is the best! So maybe in 30 years my daughter will tease me for my ridic ring setting, but as long as I still think my ring is the most beautiful, I wouldn't mind if it looks old fashioned to others!
I think in general, we tire of certain styles as the years go by. It's natural and normal. My Mother just had her 80's sapphire/baguette re-set and it's modern and gorgeous!!! Might have to post some pics.
I do know however, that if you begin with a gorgeous diamond or centre stone, regardless of whether or not it's halo'd, and choose the setting of your dreams, your desire to change it wouldn't be immediate.
I don't think I would have chosen the setting I have now 15 years ago when I became engaged- had I'd known then what I know now....well, I might have ended up with something similar, but DH insists I'd have found a way to upgrade it one way or another!!!
Princess Diana's sapphire ring was all the rage 30 years ago, and now Kate wears it. However! I do think if Kate had HER way, she'd be wearing a different e-ring entirely.