Grease a saucepan with coconut oil and place over medium heat; add rhubarb. Cook until rhubarb starts to soften, adding water if needed, about 10 minutes. Stir raspberries and 1 packet stevia powder into rhubarb; cook until sauce is smooth, 5 to 10 minutes.

Fill a pot halfway with water and bring to a boil; add tapioca. Simmer over medium heat, stirring often, for 1 minute. Reduce heat to low and continue simmering until tapioca is completely translucent, 5 to 8 minutes.

Blend coconut milk, dates, maca powder, and vanilla extract in a blender until smooth.

Strain tapioca porridge through a fine-mesh strainer and transfer back to the pot over low heat. Stir coconut mixture and 1 packet stevia powder into porridge. Simmer until liquid is absorbed, about 5 minutes more.

Pour porridge into 3 wine glasses and top with raspberry-rhubarb sauce.