I have a similar bike, though it has higher bottom bracket clearance. I think the main problem are tires. even 37s don't have much float. I was on a fourty mile section of rail trail with firm stone dust surface, and I had to let a ton of air out of the tires to get up on top of the surface. Of course, you can fit wider tires.

If you run drops as you probably "should" if you are doing a lot of road touring, there are control issues, unless you can find some dirt drops.

Finally there is braking, most drops, combined with road levers and cantis, or whatever, do not provide the kind of stick in the spokes stop I want off-road.

You could deal with the last two, obviously by simply adding flat bars and MTB brakes.

So I think all the problems you will encounter probably aren't driven too hard by the frame. I have an old 80s moutain bike, and it is pretty similar to a touring bike in it's frame. Also, some expedition bikes design for 50% off-road/road , like the Expedition 26, still have the really long stays.