This article seems to completely miss the point of design.

Design is not art, particularly as it relates to UI. Interfaces are built to bridge a need with a solution: the ATM, the calculator, elevator buttons and screens.

The reason we have trends in UI design is not because someone, somewhere, thought a really cool and fancy effect would be just what the user needed. No, trends are trends because they serve a need.

When Apple first released the iPhone they used the then-popular skeuomorphism style because they knew many people using the device wouldn't understand what made something a button vs. not. A texture, shadow, and lighting helped remedy that concern.

Now, some 11+ years after the first iPhone we see "flat" design in UIs as trendy. That's for a reason: the technology we use is now ingrained in much of our day-to-day life, we no longer need things in the screen to look like a button in order to know "Hey, I can tap this."

Timeless design certainly serves a place, but your goal as a designer shouldn't be to create something that's "timeless" or "trendy" but instead just design for the problem at-hand. That's all that matters.

I agree with the bottom line, but I think there needs to be a distinction between visual style (which the article discusses) and design.

Design does not exist on its own or for itself. To design is to serve a purpose. The notion of timeless design is then in fact a function of how well the designed object achieves its intended purpose, and for how long. A brand, product, or service that can successfully remain or evolve to be relevant and useful for long periods of time will be viewed as timeless. Visual style alone can never be timeless because to divorce it from its context is to isolate it from its usefulness. It is then left as an artifact of the ever-changing cycle of visual trends. Conversely, any style can achieve some level of timelessness if it is part of a thoughtful and principled system (brand, product, service, etc).

So, it is counterproductive to think of design only as a visual style. Form does not have to follow function, but function will always have an edge on form. It is this difference where visual style drives and falls from the trend cycle, and ultimately where function wins out.

…the way to longevity is to step away from trends and look at what has been done that has lasted.

To expand on this sentiment, it is more important to look at why what has lasted, has lasted. Consider the context of how, where and who uses it; how it all fits together; and how effectively it achieves its purpose. Designing for longevity requires constant evolution—you cannot set out to design something timeless, set it and forget it. For designs that remain to be considered "timeless" and have not changed over long periods of time, it is likely that the need has not changed either, so it is able still achieve the purpose it designed for. Timeless design is achieved through consistently and effectively fulfilling the need of purpose. If you do this, you can make it look however you want.