The “entire NXT roster” is expected to be backstage at the Royal Rumble, according to PWInsider.
There are currently 22 announced wrestlers for the Royal Rumble match, which leaves 8 spots, so there is a chance (though obviously just speculation) we may see an NXT wrestler or two join the main roster on Sunday.
Samoa Joe is reportedly expected to be called up to the main roster very soon, so there’s a possibility we may see him make his debut at the Rumble.