I know obvious "my mom's dog" concepts are unoriginal, but they ARE a reliable way of guessing what Pokemon ideas Game Freak might do next. Let's list what they haven't done yet, so we know what to expect.

>there somehow has never been a single Dark Type bat, snake or spider
>no Ice Type arctic hare
>no Fairy Type gnome/dwarf, or pink fairy armadillo
>no Electric Type cheetah
>no Bug Type based on a computer bug/virus/glitch