Note that alot of the spike recently was a stress test, it just dropped back down to where it should be under 0.4 mb. Still growing at a good clip but will be years if you extrapolate it not including the spam attack/stress test.
Sure. Disregarding the spike, even in the chart you posted, you can see the average block size has nearly doubled in one year. If that continues, we'll hit 0.8mb per block in a year or so, and that's assuming a steady growth rate. A year or so to start hitting the 1 mb ceiling seems like a safe estimate if you want to figure out what to do about it before you find out experimentally, like it or not.
