I use sucralose (Splenda) on my lemonade and it has never become to sweet. I have never used a pinch of salt, but I will probably give it a try sometime. If you can make it with Key Lime juice, it makes it naturally sweet & requires very little sugar, agave, or sucralose.
You can reduce the amount of sugar to make the lemonade less sweet or using Meyer lemons which are naturally sweeter than regular lemons and you will not need to add sugar. To make it less sour use more water and less lemons. Read more: http://www.foodaq.com/html/Cooking-Recipes/103793.html.