I think you can apply for an extension at a later date. Your approved permit will not get affected. IRCC clarifies that deferrals or leaves of absences don't affect their approval decisions.
It is indeed very strange that they have not begun issuing PPRs to full study permit applications. Do you think they are prioritizing family/ spouse visas first? It makes no sense that it has been more than 2 weeks and no movement on PPRs
That would make for atrocious PR and also result in them losing lots of money, trust, and "face". I really hope they are smarter than deciding to go down that route.