All issues marked for 0.4.0 have been closed on Github, or pushed back to 0.4.1.
Now, is the time where the community comes to play. Lutris 0.4.0 is now using Python 3 and might have new and unexpected bugs, also the icon view has been rewritten to use Gtk.FlowBox which is completely different from the previous implementation.
There are also some new runners: libretro and ags that need testing.
The only way we can ship a quality release is by testing the current code as if it was a completely new project.
So stop using Lutris 0.3.8, git clone the repo and break it in weird ways!