You can play around with it in the Sheldon Brown gear calculator if you figure out your chainring size, increase / reduce it by the ratio of the Schlumpf you want, and then input that number as the second chainring
I quite like the numbers that come out using a 2:1 ratio (44t chainring, 22t sprocket) into the Alfine with a speed drive and a 20x1.75" tire. Low of 19.7, high of 98.7. Pretty good for touring! You could tweak it towards speed, get some silly high gear inches, and still have respectably low hill climbing gears if you wanted.
The mountain drive reduces the ratio pretty severely, so unless you ran a huge chainring and a very small sprocket, i'd personally think that the reduced gear drive would be very hard on your internal gear hub. I'm not sure what the maximum input ratio on the Alfine 8 is unfortunately, but if you theoretically used a 52t chainring and a 16t sprocket, the input ratio on the reduced drive mode of the Schlumpf would still be 1.3:1, which is quite brutal. Some people exceed the input ratios on these hubs all the time, I think it depends on the user and the use. Plus, your lowest low gears would be around 13" on a 20x1.75" tire, which seems lower than what is typically really even useful. So overall, I personally think the mountain drive isn't too great in this case.