2.7 - 4.0 years, by my math, so I would agree with your assessment.

...but that's based on pre-IANA-runout rates, though, and doesn't account for the pent-up backpressure of demand. So probably a lot less, in reality.

Not even remotely worth the effort, even if there were a legal pretext for "reclaiming" IPv4 space (there isn't; there's already precedent denying it).