Great Carlo, I’m eager to work on this, just a bit overwhelmed with work these days, but in the weekend I’ll give it a try.
I think yaru-dark-theme-toggle might be a bit of a misnomer at this point. It’s not too late to change the name to something more like theme-variant-toggle. Or even the more generic but still descriptive theme-toggle, considering that in the future you might like to provide theme and not only variant switching. After all, this could be useful for people not using Ubuntu or using other themes in Ubuntu, and having to move between this extension and Tweaks is not very cool. In my mind I have something like: you define a rotation list and the toggle simply picks items in a circular fashion, perhaps with an option to follow a daily schedule. I’m not implying that that’s necessarily a good idea, but only suggesting to rename the extension so that we can keep some possibilities open. Moreover, the basic Yaru variant switching functionality is likely to be provided by gnome-control-center eventually and at that point this extension could provide richer functionality so as to make a difference for users wanting finer control. The only reason I see for severely restricting the extension to be a Yaru variant toggle is if it were to be adopted as the official Ubuntu theme switcher, but that doesn’t seem to be the case since discussion is currently focused on extending the control center instead. And even in that case a name like theme-toggle or theme-switcher in Ubuntu GitHub would be perfectly fine, so AFAICS is just a win-win situation (except for the additional work of renaming the stuff).
Also, have you considered moving this to https://gitlab.gnome.org/World/ShellExtensions?
(Btw I’m ok with the gnome-shell-extension- prefix, I just omitted it for the sake of brevity)