Hi
For me a future classic might actually be the Rega Elicit (the curved shape one).
It has an incredible design, and although it wasn't sold in buckets like the Brio-R, I see it being hunted by collectors because of its great sound and DESIGN.
I think to be a classic, the amp has to have a "singular" and unique design, or some special characteristic, like good and characteristic sound of that model for example. I don't think that technology dependent amplifiers with dacs or whatever will be sought after, because technology evolves very rapidly (like in computers), but in case of the Devialet that would be the exception because it is reference, and it will always sound good.
Best regards