According to Wrestling Observer, there are no plans for Samoa Joe being called up to the WWE main roster. The same goes for Asuka.
The purpose of these two wrestlers being on NXT is to teach the young talent and groom them for the WWE Main Roster.
That is the reason why Samoa Joe worked a storyline with Baron Corbin, and Asuka has been working with Dana Brooke. WWE has plans for both Corbin and Dana to be on the WWE Main Roster. Rob Naylor, who has worked for the NXT Creative Team, recently revealed on an Audio Show that WWE doesn’t have any big plans in store for Samoa Joe.
Also, WWE feels that if all the talented wrestlers were to be promoted to the main roster, then NXT would become a shell.