George Haynes (another pre-1950s writer) pointed to possible implications that per-capita Senate membership voting has for equal Senate representation. This matter, in fact, led Maryland delegation to 1787 convention to cast lone vote against version of "great compromise" that convention approved. Maryland's Luther Martin opposed per capita voting because it departed from idea of states being equally represented in Senate. Per capita Senate voting was proposal of delegates Gouvernor Morris of Pennsylvanis & Rufus King of Massachusetts.
Some thought this might result in principal of equality losing its value for smaller states since Virginia (largest population at time) senator might vote with 2 from Delaware (smallest population at time) leaving former with less than equal votes. Of course, Senator from Delaware might vote with 2 from Virginia. On this point, however, Andrew McLaughlin (_Foundations of American Constitutionalism_) asserts that the framers actually gave up central idea of equal representation when senators were allowed to vote per capita, and not by states.
Several decades ago, Oregon Senator Wayne Morse suggested that intent of using equal votes in Senate to give states "negative" was, perhaps, inadvertently undermined by convention's failure to require 2 senators from a state to cast unified vote. As Morse noted, roll calls in Senate call upon members, not upon states, so it possible for Senators from a state to vote against each other (Recall that Morse was one of 2 members in 1964 Congress to vote against Gulf of Tonkin Resolution and that he was defeated at next re-election bid). Roll calls in Senate are members, not states, so it is possible for senators from a state to vote against each other (issue of split Senate delegations is interesting topic in itself).
1787 convention delegate Roger Sherman of Connecticut, who made initial proposal to have second chamber apportionment based on equal number, held that equality of Senate votes was not so much security for small states as for state governments. According to Sherman, state governments could not be preserved unless they were represented and had a negative in the general government. This notion later became issue for some opponents of 17th Amendment direct election of Senators.
[[Interestingly, RS also thought that majority of states concurring should comprise majority of nation's population. And not all matters were large state-small state ones. Contra Hamilton, NY voted with small states throughout convention because majority of delegates opposed significant changes to Articles of Confederation.]]
On other hand, Sherman's concern that 3/4ths amending process might conceivably be used against particular states resulted in convention adopting "unamendability" portion of Article V. Morris moved this point and, after weeks of disagreement, delegates agreed without debate/ opposition. Virginia's Edmund Randolph, who had proposed representation by population at opening of convention, had since developed proposal to allow for both equal and proportional representation depending upon circumstances. But Randolph never brought this to floor because he had come to believe that small states would only accept equal Senate representation (as, apparently, did Madison who opposed equal representation in second branch right up to point that Morris made above motion).
Each time on this list that I've suggested there is not universal agreement re. "unamendability" portion of Article V, I've also suggested I wouldn't hold my breath about practicality of using conventional amendment process to either abolish Senate or establish unequal representation. There has never been serious challenge to equal representation so question is "academic" right now.
Independently of one another, however, political scientists Jack Peltason and Frances Lee have indicated that provision on Senate apportionment invites questions about amending language of Article V using conventional procedures and then amending provision apportioning Senate, adopting amendment providing for single legislative chamber based on population, amending Article V to have new amendment process without equal representation constraints. Neither Lee nor Peltason envision any of above coming to pass.
At moment, "proposals" to alter Senate apportionment include Michael Lind's somewhat suggestion that "mega-states" be divided into smaller units, Lind's idea to "nationalize" senators who would be elected under PR system, and Thomas Geoghegan' argument to enforce "one person, one vote" principle as US Supreme Court did with state senates in Reynolds v Sims (1964). These notions range from somewhat silly to far-fetched, not to mention lacking feasibility.
I wonder if ideas of likes of Bruce Ackerman, Akhil Amar, Mark Tushnet (whatever differences exist among them) about amending constitution outside conventional channels (Sanford Levinson may have written about this also) might be useful here even though they, themselves, have not addressed this specific matter. Michael Hoover
ps: George Will's 11/2 Washington Post column opposing abolishing electoral college ties EC to Senate and, inadvertently, makes case for getting rid of both