I tried making my own drink with date sugar + water, since date sugar is really a whole food just cut really fine, but it doesn't really dissolve, so the drink is pretty chalky and unpleasant.
I am a vegan/raw pastry chef at a restaurant and you are right about date sugar not dissolving in liquids. Also, most date sugar is processed with flour so it's not gluten free and that's another reason it does not dissolve easily. You might want to try date syrup. It is made just from dates and looks like maple syrup but not as sweet. Some of the Whole Foods sell it under a company called John Mountain. I make my own but if you can't do that or find a Whole Foods who will order it for you, Middle Eastern Markets generally sell it. I like the date syrup from Lebanon best as the only ingredient is DATES. Some of the other countries put sugar in their date syrup.
Love & Kale,
Chef AJ