I think the immediate obvious next in line superstar is Tedesco. He's already really a star, but hasn't had much team success, if the Roosters are anything close to contenders this year, his star will rise to a new level.
Cam Munster & Michael Morgan have both had some good years in recent times, but you probably wouldn't call them superstars yet, if they keep getting better in the coming seasons they could be next in line.
Guys like Matt Moylan, Shaun Johnson & Tuivasa-Sheck are all star level talents but have fallen off the radar, if they just have 1 good season they will immediately be up there again. Johnson is a golden boot winner, he could be anything if it clicks for him. Pearce & Cherry-Evans could be close to the best halfbacks in the game if they keep some form up when Cronk & Thurston go. Milford is another who has star potential but just seemingly doesn't want to realize it. Barba & Radradra if they return. Valentine Holmes & Jack Bird could be stars if they can master a spine position.
Then the next generation of guys who are too young & haven't done anything in the game yet to be considered stars, Tom Trbojevic, Cleary, Ash Taylor, Ponga, Moses, Croft, French, Latrell Mitchell if he find his way to fullback again, maybe Lamb if he can get back into our top side. 12 months could elevate any of these guys. Whoever reveals themselves as the premier hooker out of Levi, Brandon Smith, Jayden Brailey & Lichaa is likely to be up there too. Exciting times.
EDIT: Taumalolo is another obvious one, pretty much the only forward in the game capable of being seen as one of the game's true superstars.