Block size could reach the 1mb limit at any time with a massive influx of users and
the chart for average block size looks like it could possibly have a sharp exponential rise hitting the limit within a short period of time, well before March 2016.
IMO, even Gavin may be to late. Most likely, if this increase in adoption happens, transactions will be pushed off-chain to Coinbase and other services until the limit can be increased. Anybody opposed to the block size increase doesn't even have a working solution for scale, so I don't see how their arguments can even fly.
furthermore, no one wants to use Coinbase to buy their cup of coffee p2p. they just won't do it.
Bitcoin needs to do an Uber and scoop up as many users as fast as possible round the world before gvts, regulators, and banks can stop it. we may already be there fortunately but we do have a ways to go and it's clear that 1MB is an artificial cap on growth.