1) load user theme from gresource file like gtk (~/.theme/<theme name>/gtk-3.0/gtk.gresource)

I think, this can be do in 'user theme' extension.
Some file can be put in gtk theme(in 'gtk.gresource' file) and used in gnome-shell theme.
But if change gtk theme  -- gnome-shell theme is not applied correctly or not applied.
Please, implement load gnome-shell theme resources from file
~/.theme/<theme name>/gnome-shell/gnome-shell-theme.gresource


2) Also implement settings somewhere load user theme globally.

To change user theme now i can put theme file 'gnome-shell-theme.gresource'
to /usr/share/gnome-shell/ directory to change style globally.
It will be great have easy way for this.

> _themeResource = Gio.Resource.load(global.datadir + '/gnome-shell-theme.gresource');

May be build 'global.datadir' with some environment variable?

Like this:

> let themePath = global.datadir + '/' + GLib.getenv("SHELL_THEME_NAME");
>
> themeResource = Gio.Resource.load(themePath + '/gnome-shell-theme.gresource');

or 

> let themePath = global.datadir + '/' + GLib.getenv("SHELL_THEME_NAME");
>
> themeResource = Gio.Resource.load(themePath + '-theme.gresource');