If there's an 812 Superfast convertible on the way, the question is whether it will be another severely limited edition. Ferrari has lately been at its most restrained with V12 series production convertible models. The most recent was the F60 America, based on the F12 Berlinetta. That model was for the U.S. only, and Ferrari built 10. Before that, Ferrari made 80 examples of the 599 SA Aperta; this is the company that built 209 of the LaFerrari Aperta. The Ferrari 575M Superamerica, the first Ferrari with an electric hardtop, got 559 examples, and the brand made 448 models of the 550 Barchetta Pininfarina in 2001. You need to go back to the 1973 365 GTS/4 for the next-most-recent droptop V12.
As for the roof mechanism, another forum member said he'd seen the car and the roof opens in the style of the mid-engined 488 Spider. On the Portofino, the entire rear decklid raises, the roof and backlight split in two, and a folding truss lays them upright in the trunk. The 488 roof also breaks in two, but it flips around hinges atop the B-pillar, resting upside down in a space above the engine. Mimicking the 488 for a front-engined GT would evoke the 575 Superamerica. That glass roof and backlight on that car were one piece that rotated around the B-pillar axis; when the roof was open, the underside of the roof was exposed. A bit of trivia: Leonardo Fioravanti designed the droptop 365 GTS and the roof mechanism for the 575 Superamerica.
Yet another forum member said he attempted to place a deposit on a convertible 812S, but his dealer didn't know anything about the car, which isn't surprising.
Forum user gt_lusso wrote that the 812S Spider will come within 12 months. If that's not enough hearsay for you, the same user said "a very reliable source" told him there's a Portofino Coupe coming, that the 488's successor will debut next year and get a twin-turbo V8 hybrid, not a V6, that Ferrari V6 models will comprise a new lineup under the V8 cars, and that more vintage-inspired designs are on the way.