I hate the term future proof. No one can possibly know what the future will look like. What may work today may not be working tomorrow.
The only thing we can do to predict some kind of future is to base it on the experience and knowledge we have about the past.
This is how statistics works, by gathering numbers from the past we can draw an imaginary line of how things will look like tomorrow. But still, no one can ever be sure. That's why I for instance don't like salesmen who tries to make a deal by claiming that their latest television set is future proof because it has a lot of HDMI inputs. If it's something that history has shown us, is that technology doesn't last.
It evolves, but it doesn't stay in it's current shape. To continue on the technology stride, I remember the war between Blu-ray and HD DVD, a war that Blu-ray eventually won. After that it was said that if you wanted your new computer or home theater to be future proof it needed to contain a Blu-ray player.
This was 4 years ago. How many still believes that Blu-ray is the future? The same story goes for websites. Many people today say that they're building websites that are future proof. That's a lie. We can't create future proof websites.
What we can do though, is to think in a future friendly way when we create websites. Flexibility is one of the most important aspects for future friendliness. If you have a simple robust framework that can expand and contract on demand you have something that is truly great to work with for the future. If you want to achieve flexibility you need to focus on what matters.
Don't go ahead and build the Titanic (it was supposed to be future proof, right?). It will take you a lot of time and resources, and by the time you're done the future has already changed. Instead go ahead and create yourself a little rubber boat which can easily change course when needed.
Make quick turns, embrace the uncertainty and learn how to adapt to new things when they come your way. Be flexible. Be lightweight. Be future friendly. Because the future can head in many directions.