If you are just saying that you want to try plasma wayland than install plasma-wayland-session
And wayland-protocols too..
(you just need to install it and then change to plasma wayland from log in screen)
sudo pacman -S wayland wayland-utils xorg-wayland plasma-wayland-protocols plasma-wayland-session lib32-wayland
all packages that are crucial for wayland to work properly are in this command 