The ability to sponsor parents is HIGHLY uncertain - not clear what government's going to do with this at all, subject to long waiting periods and random chance as partially it's a lottery, and long-term requirements to show income above a certain level (by the applicant i.e. your son), and many end up surprised years later discovering whoops, their income in some period was insufficient.
And a possibility or likelihood that government could suspend, restrict further, or cancel altogether.
In short, would be foolish to think that is any more than a small chance. Not impossible, but basically only hypothetical if you're talking years in advance.