Burt Neuborne has posted this draft on SSRN (forthcoming Stanford Journal of Civil Rights and Civil Liberties).  Here is the abstract:

Professor Neuborne argues that the modern filibuster functions as a de facto supermajority voting rule that violates the one Senator-one vote language of the 17th Amendment, and the unamendable equal state suffrage guaranty of Article V. Just as a weighted voted system in the Senate would violate the equal suffrage guaranty, He argues that the inevitable mathematical variation in the value of each vote under a supermajority rule condemns the modern filibuster as a violation of the equal state suffrage rule.