IM NOT A ENDLESS MOBILE EMPLOYEE, BELOW ARE JUST MY PERSONAL OPINIONS
As for GNOME 4
With the current EOS, it’s almost vanilla GNOME enhanced with a few Extensions, which make up the different look (similar to the approach Ubuntu or Mint uses)
eos-desktop@endlessm.com
eos-hack@endlessos.org
eos-onboarding@endlessos.org
eos-panel@endlessm.com
eos-watermark@endlessm.com
force-quit-dialog-extension@endlessm.com
ubuntu-appindicators@ubuntu.com
I really hope that Endless keeps their UI Look and Feel, it simply works as people expect it to work from what i get feedback from my local community.
As for the Dark Theme
Endless OS already uses just plain Adwaita as shipped with the current Gnome used, so it’s already possible, but not through the GUI. Run the following command:
mkdir -p ~/.config/gtk-3.0
cat << EOF > ~/.config/gtk-3.0/settings.ini
[Settings]
gtk-application-prefer-dark-theme = true
EOF
gsettings set org.gnome.desktop.interface gtk-theme 'Adwaita-dark'
Now, all applications which support it are using the dark Adwaita variant.
As for the NVIDIA part
This will IMHO depend on success of the upstream developers. NVIDIA is completely doing their own thing with their proprietary drivers (as opposed to Intel and AMD) and is simply lacking the mechanics to support Wayland currently. However, there are initiatives to somehow make Wayland run on Top of their drivers with all the benefits like real good performance: https://wiki.gnome.org/Initiatives/Wayland/NVIDIA