Two tones make sense to contrast islands from the perimeter cabinets. Also helps when you want dark cabinets and space is confined, you can then use the lighter finish on the uppers. All depends on the space and the colors.

On trend right now. I think it also depends on the size of the kitchen, it can look overdo if the kitchen is small to medium sized & also depends on the other elements, i.e.cabinetry counter tops etc. Good luck.

We do a two veneer kitchen right now. Uppers with a beautiful Korelian birch burl veneer, which is relatively busy, and keep the lowers grounded and calm with a more "solid color" wood veneer like maple quarter cut. In a classic modern wood kitchen I would not consider two tone a fashion.

I saw lots of two tone cabinets on the recent Parade of Homes - usually darker stained lowers with white uppers. If you like the look, it doesn't matter what is on trend in 5 years - marketers should not be determining what you like. It is fun to look at new stuff and new ways of doing things and add them to your home if in the budget and works. But, if you know what you like, your kitchen will make you smile whether it is on trend or not. I recently put in a farm sink because I love the size and look, but my cabinets are old fashion and out of date. That doesn't bother me a bit because I like them.