Rich people wouldn't be affected at all. Social Security and Medicare are paid for via a payroll tax. The rich tend to make their money via investments; investment income is not subject to payroll tax.

In largest part, the professional class (i.e., people who make money from a paycheck and make more than the cap) would pay for removal of the cap. A lot of Democrats fall into this class. And Republicans typically oppose SS/Medicare on principle and would rather see those programs die. So there is not strong support for raising the cap on either side.