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The EPI article as well as this thread is a bit dated, although Dragon's post from 2013 is still applicable. Hillary Clinton's approach today is more comprehensive:
Hillary Clinton: Social Security and Medicare
She would expand benefits and get "the highest-income Americans to pay more, including options to tax some of their income above the current Social Security cap and taxing some of their income not currently taken into account by the Social Security system."
If you are really going to ask the wealthy to pay more, then taxing much of their unearned income (capital gains, dividends, etc.) would get sizable increases in revenue. However, I can see a very difficult uphill battle to make that happen in Congress. It would need a mandate in both Houses but also a 60 vote veto proof majority in the Senate.
While all of these feel good measures might buy votes, it is one reason why the public has become cynical of our government when candidates cannot deliver on their campaign promises because of petty tribal politics.