The downside is the huge geriatric population will need more and more resources until that situation becomes part of the new stable norm.

That exactly is the problem. When half the population is too old to work, who’s going to be providing for them all? Someone still needs to produce stuff.

It could be Japan is entering a stable period where needs and resources are predictable and known. Sounds like a higher standard of living to me.

Good luck predicting human needs and behaviour.