Working in a domain that is the epitome of luxury, I have seen that the face of luxury is changing over time. The old concept of luxury was created by a scarcity of materials: gold and diamonds were rare in those days. But of late it seems that those materials are not so rare anymore.
Firstly there is the fact that the materials do not degrade over time, so the existing stock of the world's luxurious materials at least stays constant: this was the inherent reason why our forefathers desired these materials for value retention. Constancy in an expanding world would not be so bad...
Were it not that secondly some of these luxurious materials are at the verge of being synthesized: diamonds can be man-made now and who knows how many gold and platinum-filled asteroids can be harvested in the coming decades...
Combine the last facts with the fact that more and more of the world's population is aspiring to the material luxury and the material supply is also enabling that aspiration, and you see that material scarcity is an illusion that is only veiled by the desire to aspire.
So what scarcity will define the next luxury?
According to me the next scarcity is going to be human. Let me explain: our lifespan is still capped; In an age when we will be able to design or customize everything we want, time to do so is going to be the ultimate scarcity... We will only design (or co-design if you are less creative) the things that we feel passionate about, customize the things we like and the "meh" products we will buy off the shelf. This is the scarcity of human attention.
Now if you can not design the product yourself, you will pay dear money to have an expert design it for you. An average designer is fine, but the true luxury will come from convincing busy people to take time out of their regular life and design that little special thing for you: say ask a manufacturer of slow cars to make a race car and then name it after his daughter. That would be another human scarcity: the scarcity of human expertise. This scarcity is becoming very obvious in the watch-making industry where watches hand-made by Swiss watch-makers are fetching significant premiums due to the scarcity of that expertise.
This does not mean that gold and diamonds will lose their value overnight and that you will still need a golden wedding ring with diamonds for the church to bless (if there is such a thing as church left, but that is not for discussion here!)... But a nice saying, I recently overheard said: "You will own less, but with more value."