I may have a somehwat narrow view because my first carbon road bike was a Specialized Roubaix SL4 Disc. It cleared 28/30mm labeled tires, had disc brakes and built in compliance in the frame. That was 10+ years ago and arguably still a relevant bike today.
Doesn’t look like the SL9 is one of them. I compared the frame geo numbers of the Tarmac SL6 and SL8 and barring for some minor adjustments to accomodate bigger tires I don’t see any major adjustments and would assume the SL9 to be in that same ball park in terms of stackheight and reach. It will fit 20yr old racers perfectly and that’s who those designs have in mind.
If you’re increasing tire clearance from a 32mm tire to a 40 and beyond is where you start changing the use case for a roadbike imho, but that’s another category “allroad” - e.g. Canyon Endurace, BMC Roadmachine and the like. I don’t see Specialized doing that with the SL9. This bike is another iterative update and will be marketed as lighter than the SL8 but more aero, while increasing tire clearance by 2mm, nothing ground breaking and just the expected updates.
I road fire roads on my Tarmac SL6 on 25mm tubeless tires from time to time and it was fine - sure 30+ is more comfortable but the intended use case of a Tarmac is still a light and aero Racebike not an allroad bike.