Where this gets even more interesting is: Some transmasc Pikachu art features the two sections of the "heart" tail stitched together. As for how the transfem Pikachu counterpart to that would work, my guess is that it would involve reshaping of the tail.
As for Pikachu tails on Pikachus that are not male or female look, there are several ways people draw those: Some are drawn in a way that differs majorly from heart or square tails, one example being a mostly-triangular end, somewhat modeled after flames. One intersex Pikachu artwork I saw is one where half the tail is heart, the other half square. A theoretical ADDITIONAL way to draw a non-masc non-fem Pikachu tail is for the tips of a heart Pikachu tail's hearts to be a shape that is not round, so something like a triangle, square (so a notched square tail), or something else, or to have the entire tail end be an arbitrary shape. Or you could have the whole tail end in a circle. There are MANY ways to draw a Pikachu tail that is not masc or fem.
Also, things can get even more interesting to think about when we throw intersex into the equation.