I can only speak for my 2011 model which I understand is similar. The fork and wheels seem different now. Our bike is set up for road touring.
The frame is very solid and stiff. Only when we loaded it with the most luggage I could attach to it, I noticed a little frame flex.
Our wheels are strong 48-spoke wheels but I think they are different now. There is plenty of clearance and I think you will find a few threads on this in this forum through a search.
We have front and rear racks and full fenders on the bike. Rear rack is no issue, front rack requires working around the missing mid-eyelets. For the fork we have, there are some good options, but I have no experience with the new style.
Fenders work, though again the fork required a little bit of hacking for us on the fender side.
If you put adequate tires on, I don't think this bike still be an issue in soft off-road conditions. Will the gearing be low enough for what you are looking for? Will the ground clearance be enough?
You can often read on the forum, that the cannibals cannondale rides more like a tank than something very nimble (Calfee?). While I have never ridden much other than the Cannondale, it does ride very stably (tank?). It is fast.
With rack, fenders, and the odd accessories, we are at 20kg.