Well admittedly, the off-road trails rarely go anywhere. But there are a few that go through. Would be interesting if you could designated things like levy roads and dirt roads that have a surface that's fine for fat tires but no good for road slicks.
I've used the road alongside the bypass canal a couple of times in the past to go from Flatwoods down to my aunts place in Thonotosassa. Shortcuts like that should probably be included, maybe in a different color, but probably shouldn't be routed by default.
Crushed rock roads like that are quite navigable with 28 mm tires but I couldn't see most people with riad bikes trying it. so there's definitely a middle ground where it depends on the rider. I wouldn't try it with the 23s on my fixed/ss. The 1/8 mile dirt road to my Aunt's place is super sketchy with the 23 mm tires even though it had been graded and packed.
Obviously they're only including paved surfaces for now.