The short version is "it depends". Essentially, each separate Wayland compositor needs to add support for the nvidia driver (or the driver needs to support more standardized APIs).
Gnome and KDE support Wayland on nvidia hardware (though it's a bit rough around the edges). Wlroots (and therefore Sway) doesn't because they don't want to have a separate code-path for one driver which doesn't want to support standards and because the APIs the driver does support wouldn't work well with the code model of wlroots.
Gnome and KDE support Wayland on nvidia hardware (though it's a bit rough around the edges). Wlroots (and therefore Sway) doesn't because they don't want to have a separate code-path for one driver which doesn't want to support standards and because the APIs the driver does support wouldn't work well with the code model of wlroots.