Oh I wrote this way back in 2004 in the old delphiforum days. So I am sure the PAP already knows of this idea a long long time now. They are just waiting for those flats to reach those ages.
If the PAP is worried about being able to hold on to power they might also start to have cheaper flats but with substantially shorter leases. Instead of 99 maybe 60 years. How that will affect the broader property market I don't know. But certainly banks may get more anxious to offer mortgages to HDB owners.
It will be good business. Extend the leases. Tell people you can use CPF to pay for it (thereby reducing a large chunk of CPF burden)