Recall that a constitutional amendment providing for the direct election of U.S. senators was first proposed in 1828. The effort to amend the Constitution is not a race for the short-winded. But a constitutional amendment may not be needed. Even without a constitutional amendment, presidents today are de facto elected by a vote of the general public. The names of the presidential candidates, not members of the Electoral College, are on the ballots.
Some states require electors to promise their support for the candidate to whom they are pledged.
Moreover, years before there was a Seventeenth Amendment providing for direct election of U.S. senators, many states allowed their voters to choose Senate candidates. We should expect the proponents of term limits to lobby for similar statements on the ballot for U.S. representative and senator. There is every reason to believe that such voluntary pledges, over time, would take on the force of law. There is nothing unconstitutional or even unusual about placing such information on the ballot. Ballots have listed party membership for years and the experience of the Progressives in Nebraska, during the early part of this century, demonstrates that pledges are also appropriately placed on the ballot.