I've recently been playing with front suspension on my old rigid 26" mtb. That's coupled with a sprung B67 seat. I've never used such a fork before and, while it is heavier for sure, the dampening of jarring on some surfaces is pretty cool. There is some stuff I can roll over at a decent clip that I would have formerly had t go very slow for and washboard also seems a lot better.
I could see a light duty suspension fork on a gravel bike. It seems MTB is has split off towards downhill/technical and gravel or all roads is the new genre for non paved road surfaces and a rigid dropbar road design doesn't really capture all the variations you can find there.