That will 90perc. be related to GI (particularly clamping) and Tonemapping.
But also... F-Storm doesn't have correct glossiness curve, in fact it's wrong. It can make nice looking materials, but the are absolutely not PBR :- ). Ask Johannes or Daniel, they would love to change this.
So if you're asking for even more tweaked GGX behavior, it will look just slightly bit more advanced than what Corona currently has (maybe 5perc. difference?) but absolutely not like F-Storm material.
Corona's PBR will bring different UI and parameters. It will make a creation of materials easier and more like current industry standard.
They will look absolutely the same though (with exception of Sheen parameter for fabrics). Unless they change fundamentally something under the hood for BRDF, which they could...like Lambert Diffuse is getting pretty old.