Assuming a straight line. Such things are more likely to be a curve, with increasing decline over time.
However, I agree that the panic over SSDs has been overstated, and they should last much longer than the useful life of the Mac as a whole.
Even without the "swapgate" non-issue, some Cassandras have been prophesying the doom of small SSDs in Macs with little RAM -- but Apple has been selling such models for well over a decade.