While I see the probability of some form of SS means testing in the not too distant future, simply tieing it to net worth could be a mistake. First, for many people, a big portion of their net worth is in the value of their home. By retirement age, many (probably most) people have paid off their homes. In some parts of the country, that home can easily be worth well over $500K (that's a small home in places like San Diego). Unless you take out a reverse mortgage, you can't get income from that property, so means testing someone out of SS under those circumstances wouldn't be a good idea.

Also, a fixed limit like the $2 million you suggest has other problems, even if you discount the value of someone's home. If you could get 6% on $2 million, that's $120K a year before taxes. Not too shabby, but if the amount isn't adjusted for inflation, in 20 years or so, the effective value would be half or less of what it is today. I don't know too many people who'd consider even $120K a year (about $90K after taxes) as rich, much less the depreciated amount.

My guess is that one of two things will happen. 1) the government will means test anyone who actually managed to save for their own retirement (401K, IRA, etc) by calling them "rich" and therefore not deserving of SS benefits. However, this could lead to people wanting to string up politicians. My guess is that 2) the taxes on retirees with income other than SS would be raised again (Clinton and the Democrats did it in 1993) to effectively give someone a SS check with one hand and tax it away with the other.