I bake quite a lot and I can tell you its impossible to make a nice, low carb meringue. Sugar gives a textures (that crunchiness ) and there isn't any sweetener that can replace it Im afraid. Ive tried everything. The best result was with xylitol but it wasn't a typical meringue. Just a soft, cloud like kind of sponge.
The best for baking is xylitol, in most cakes Splenda is ok too. It doesn't have aftertaste like Stevia (which is good and natural but I hate the taste)