Volokh co-conspirators Orin Kerr and Jim Lindgren have come out in favor of a proposal to limit the terms of US Supreme Court justices to 18 years. Co-conspirator Randy Barnett is also somewhat sympathetic.
My response: why not 4-year terms for Supreme Court justices, commencing at each presidential inauguration? To paraphrase Shaw, we've determined what they are--now it's just the duration we're bargaining over.
The justifications for 18-year terms--that they might make the Supreme Court more "modest" and responsive to public opinion, and presidents less inclined to appoint young, inexperienced justices, in the hope of influencing the Court for 50 years--effectively concede the point that the justices' role has long ceased to be anything even resembling neutral, dispassionate application of the Constitution and federal statutes. It is apparently now widely acknowledged that candidates are nominated by politicians for the sole purpose of enshrining particular political viewpoints--even constituencies' interests--in Constitutional and statute interpretation. Given, then, that the justices' role is a de facto political one, what's the argument for not making them every bit as accountable as any other political actor?
Of course, once they're political actors, it's hard to see what benefits they provide that aren't already covered by the other democratically accountable branches of government. Then again, perhaps if they had simply stuck to being judges in the first place, and hadn't succumbed to the temptation to abuse their powers for nakedly political ends, then they might not seem so utterly superfluous now.