I'm not sure which part he's playing, but my hope is that he will replace Pine as Kirk. For anyone who thinks Shat is too old, remember:
1) Shat still looks really young.
2) If necessary, CGI could be used to make him look younger.
3) Shat has played young-Kirk before. In fact, he has way more experience than anyone else in the role. How could anyone say he can't play young-Kirk? It's just not logical. He's done it before, he can do it again.