Is every Xayah and Rakan splash art going to be featuring them together?

I would not be opposed to this, cause why not. They are kind of meant for (and to be with) eachother.

The quick answer is yes. The long answer is that they are to be together in every splash art equally just like Kindred's Lamb and Wolf are.

They did mention that with their whole theme being Duo'd they would probably have the same skin themes, so pretty sure they will do the same with the splashes if they can.