Soldato
Ask the FIA. They govern a lot of Single Seater series' yet only seem to think that F1 drivers heads are worth protecting.
It will filter down. It will take time, but F1 has the budget, resources and design to implement it sooner and influence it. Lower formula would always be later to respond, presumably as their cars often carry over for seasons on end and it's harder to design into an existing car, assuming it's not just something where a hinge is bolted onto the chassis (which could compromise the safety cell itself if it wasn't designed for it).