The filibuster is purely a parliamentary procedure voluntary adopted by Congress and has no basis in the law, so the courts won’t touch this.
With all due respect, I’m not commenting on “the RULE” in the Senate. What’s UNCONSTITUTIONAL is the handling of ELECTIONS is left to the STATES ergo it (passing such a blatantly unconstitutional LAW (not rule) WILL GET LITIGATED and that litigation will, most likely, START with an injunction that tolls the EFFECTIVE DATE of such a “LAW” until a trial is held and even then they could toll it until the Supreme Court Rules on it which could take years. In 10 months we will have an all Pub congress, most likely, and then the LAW will get MOOTED faster than the road runner.