Depends on the system if it is parasitic or not (this is good explanation on parasitic game design https://www.youtube.com/watch?v=xwHJqXKwRKM ), if they create a system that intends to last longer than a single expansion that they can build on, Mythic plus was a system sort of like this but let us take something more casual orientated and desirable -Housing-. You could integrate all sort of core systems into that, like professions, PvE content rewards etc.
It is not a matter of having an expansion system in but how this system works with everything else and if it actually is build to outlast the current expansion.
As for it tanking or not borrowed power three times in a row is starting to show the cracks equally if not worse than power creep was.