So here’s a not-so-wild thought: ABC should announce that May 20, 2009 — or, if they’re feeling greedier than usual, May 26, 2010 — will mark the last episode of the network’s “Lost.”

Species of television continue to evolve. The miniseries, for example, has essentially faded from existence beyond its Emmy category, to be replaced by two-part, four-hour movies or longer runs now labeled “limited series.” In either case, it’s a far cry from multi-night events such as “Roots” or “Shogun.”

What appears to be needed is the “maxi-series” — a program that, even in success, runs a finite number of years before coming to a resolution — providing an answer to the open-ended commitment of serialized dramas.

Not every series merits this sort of treatment. That said, setting a “date certain,” to borrow a current political phrase, for paying off the mystery in “Lost,” the chase in Fox’s “Prison Break,” the threat of Armageddon in NBC’s “Heroes” and CBS’ newcomer “Jericho” would go a long way toward forestalling the frustration that frequently besets marginal viewers of such shows, where each opened door inevitably leads to another long hallway.

The maxi-series concept reflects a push away from the traditional “Run five years and cash in on syndication” model, but so what? The old road to riches is increasingly irrelevant for the aforementioned series, which cash in on DVD and ancillary sales at their peak but whose shelf life is far more limited than repeatable franchises such as “Law & Order” or “CSI.”

In a sense, feature films have already lit the path leading in this direction. Think about the “Star Wars” and “The Lord of the Rings” trilogies, which promised a complete story with a beginning, middle and end — stretched out, by virtue of the interval between sequels, into a six-year span.

The beauty of the maxi-series is that it would allow producers to plan and build toward an actual finale — reducing, if not eliminating, the pressure to keep pulling narrative rabbits out of the same hat. No wonder the creative masterminds behind “Lost” joke about a “zombie season” when they’ve theoretically exhausted every narrative trick and, all bets being off, fill the island with zombies.

“People are fed up. They want answers, dammit,” exec producer Carlton Cuse joked on the preseason podcast, a video diary he tapes with partner Damon Lindelof for those fans whose ardor can’t be sated by a weekly hour of TV.

Beyond movies, pay cable also has tinkered with the maxi-series template. Take HBO’s “Rome,” which will return for a conclusive 12-episode run early next year. Part of that, admittedly, stems from the show’s prohibitive expense and the fact that the pay net’s European partners balked at further seasons, but a second flight of this classy drama — knowing that’s all, folks — is still an eminently enjoyable prospect.

This isn’t to suggest the maxi-series comes without drawbacks. One network exec told me the exit-strategy proposal sounds good but, as a practical matter, is unlikely to catch on — namely because nobody wants to commit far in advance to removing a series from their lineup when it might still be packing in viewers.

Granted, programmers would have to swallow hard before bidding farewell to a powerful franchise like “Lost,” or even a reliable role player like “Prison Break.” Yet the counter-argument is the near-term benefits should offset such concerns — especially if more people stick around, instead of drifting away, because they know precisely when the payoff was due.

San Francisco Chronicle critic Tim Goodman recently surmised that, separated from TV’s business demands, a premise like “Lost” would run only two or three seasons. Generously, my targeted farewell date would extend through the last night of the May sweeps in year five or six, giving development staffs time to get cracking on worthy heirs.

So come on. Tell us now when we’ll learn what’s really behind that island, when “Prison Break’s” brothers will reach safety in Mexico (and possible unseat a sitting U.S. president), and when we’ll discover how much of the U.S. survived the mushroom clouds that left the town of Jericho standing.

Until then, I’ll be sequestered in my own private hatch, getting the popcorn ready.

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