What's the Wayland equivalent of ~/.xsession?
There isn't one. You just run qtile start -b wayland from a virtual console, and that's it.
Whereas with X11 you needed to use xinit as a launcher to coordinate starting both Xorg and the window manager side-by-side, with Wayland you usually have a single "compositor" performing both tasks in the same process – in other words, the WM is its own display server.
To start applications together with the compositor, use Qtile hooks.