which is why we pop the cap in my plan. as upper income earners will now be recieving a
larger percentage of their pay back tax-free than they are losing to FICA, this will give them a net benefit up to $604,000, and thus keep them from engaging in tax-avoidance schemes that tend to depress revenue collection in the face of rising rates. so you get the actual benefit of a real, statically scored, tax hike (this usually never happens).
however, you are probably right that in addition we will have to hike the retirement age a couple of years and/or tie benefits to inflation. which is why i gave the figures in inflation-adjusted terms and provided those alternate retirement dates in my OP
we may face a temporary reverse-flow from the general fund to social security, which would necessitate spending cuts in other areas (Paul Ryan's 2012 budget is a great place to start), but which would also quickly be reversed as people began to retire for whom
there was no liability at all. that's what makes this thing sustainiable in perpetuity.