If we had the technology to freely form diamond, then it’s exceptionally hard, has incredible chemical resistance, among the very best thermal conductivities of any material, and it isn’t particularly heavy.

Being able to coat the inside of chemical vessels and pipes with diamond would hugely increase their lifespan, a heat exchanger made out of it would be incredible. Great for food processing, since you’d be able to clean it easily; great for abrasive or highly acid / alkili materials that corrode everything else. Probably awesome as a base layer for semi-conductors, as it would be great for heat dissipation.

But we are probably talking about nanotechnology to lay it down in sheets, which we don’t have (yet).