I am the Kat that Walks By Itself

I've read that Stevia will make the ice cream hard as a rock and so need to add it at the end when the ice cream is nearly done.

I don't think Stevia makes things worse, it's just that it doesn't contribute to making the ice-cream softer. I suspect that the people who warned against Stevia were expecting that Stevia ought to behave like sugar and were burned by that, because they didn't know that sugar contributes more to ice-cream making than just sweetness.

The two main things that contribute to making ice-cream more "scoopable" (that is, not so rock-hard after you've had it in the freezer for a while) are fat and gums (gums are things like gelatine, Xanthan Gum, Guar Gum etc). Sugar contributes too, because it helps make it softer, but fat and gums help preserve the fluffiness. Obviously with low-fat icecream one wishes to avoid the fat, but one doesn't want to put too much gum in, because it can make the ice-cream rather rubbery in texture if there is too much. Also, I think dairy solids contribute a bit too, because I've noticed that my low-fat ice-creams tend to be creamier than my sorbets.

Have any of you done this since this thread was started?

I haven't been making any ice-cream recently, because it's winter here, but take a look at the other posts with the tag food:ice cream experiments, which I posted since this thread was started.

It sounds like, from this thread, that you may be able to cut down on the amount of these two in comparison to table sugar.

Correct; in comparison to table sugar, one doesn't need as much Xylitol or Erythritol to get the same effect on the freezing temperature. But I'm afraid I haven't done a recipe-for-recipe comparison. It's probably easier to compare sorbet with sorbet, because normal ice-cream gets its temperature-alteration from both sugar and fat, while sorbet has no fat, and thus gets its temperature-alteration purely from sugar.

Okay, here's this BBC mango sorbet recipe and my mango sorbet recipe. Note that my recipe uses 8 tablespoons of sugar-alcohols, and the BBC recipe uses 250g of sugar. According to this conversion chart, that's 115g versus 250g: a bit less than half. That meant that I didn't need to add lemon juice to cut the sweetness.