Personally, I think RB are playing Russian Roulette with a low downforce set-up given the forecast - the old "win or crash" thing. If it stays dry, they *may* pull it off, and everyone will be saying they're genius. If it's wet, the car just simply won't have the grip, and Max could end up decorating the scenery in quite a big way.
I guess, being so far back in the championship they've nothing to lose by trying something a bit crazy.