At the winemaking club I am a member of, one of the members did a test with stevia, saccharin, and some other unfermentable sugar I can't think of, off the top of my head. These were all backsweetened to the same extent and then aged an appropriate amount. Long story short, is that all of the alternative unfermentable sugars presented some kind of off taste to the majority of the folks in attendance that evening. As always YMMV.