It is unlikely that there would be a successful suit in this matter since the Supreme Court has no power over Congressional rules wrt Congress's membership and/or rules.
Separation of Powers pretty much rules out any such suit.
Since these matters are explicitly given over in the Constitution to Congress my bet is no court would declare Congressional actions regarding membership to be "unconstitutional".
But they are not exclusively given over to Congress. The 17th A. gives the power to fill vacancies to the State Executive. If the State brings the case that this constitutes a vacancy, then "[i]n all Cases ... in which a State shall be Party, the supreme Court shall have original Jurisdiction."