The phrase "worthy successor" means someone who is considered deserving and capable of taking over a particular role, position, or legacy from someone else. Full definition
Since then, I've been on an endless quest for the true, worthy successor of that classic game. (gamingtrend.com)
Whether or not the G5 / G5S and G5 Plus / G5S Plus make worthy successors to the Moto G4 and Moto G4 Plus should be irrelevant to the software upgradeability of the G4 lineup, especially when Motorola explicitly mentioned Android Oreo update for the G4 Plus (at least). (xda-developers.com)
Super Mario World was as worthy a successor as you could hope for, with upgraded graphics, new moves, new powerups and smoother controls thanks to the power of the SNES. (snackbar-games.com)