Congress could raise the number of justices on the court to 100 and require 2 from each state.
Without the 17th Amendment most of the Justices on on the USSC wouldn't have ever been confirmed by the Senate.
State Legislatures would have replaced a Senator who relied on their own personal "wisdom" rather than doing what the folks back home wanted done. Senators would walk the staight and narrow on very visible things like court appointments and most other things as well.