alt Hacker NewsThere are 16 /8's in the class E address space that were never allocated, and 19 /8's (by my count) allocated to individual companies. If you waved a wand and returned all of that space to IANA for allocation, you would have staved off IPv4 address exhaustion by... about 3 years.
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).