TL;DR

Just for fun, I’ve been thinking about a generic layout for playing cards.

And here it is:

The available slots are those with different colors. so that the card can be rotated upside-down and keep the same face to the player.

Units can vary in the two $X$ and $Y$ dimensions, allowing for different card aspect-ratios. So the $1$ may be of different actual lenghts in the two dimensions.

The choice of $K$ allows adjusting to one’s preferences. The picture shows $K = 5$.