It's hard to see this happening any time soon. Still, if we have another decade like the 90s, when the GOP held up so many of Clinton's nominees that emergencies were declared on a number of federal appeals courts and the usual rules regarding the composition of panels were suspended, people may consider the situation serious enough to negotiate a "cease fire" over nominations, and fixed terms could play a role in a negotiated solution.
(The current fight over filibusters isn't likely to lead to a cease fire along these lines. First, the number of vacancies is quite small right now, so no matter how much Republicans and their house pundits talk about a "crisis," Democrats cannot be persuaded that such a crisis exists. Second, and again despite their public rhetoric, Republicans know that the status quo is working quite nicely for them at the moment, as Bush populates appellate courts with lots of reliably conservative and often quite young judges, so term limits is the last thing they'd want on the table. We'll need a return to control of the Senate by the party that doesn't control the White House, and a sequence of events in which both parties have been on both sides of the fight often enough to decide that a negotiated peace is better than an ongoing stalemate.)