Part of the problem is purely rhetorical: What, exactly, does "in print" mean when most contracts actually cover — and all publishers demand that they cover, at least in the early stages of negotiation — both ink-on-paper and POD printed versions, not to mention electronic, audio, etc. forms? The industry as a whole would be better served, both rhetorically and legally, by adopting more-accurate terminology, such as "revertable."
That said, there's a very simple solution to the problem that actually simplifies matters for everyone. Instead of a traditional OOP clause, consider something like this (cribbed together from two different contracts):
The Work shall become Revertable if, at any time more than eighteen (18) months after its initial date of publication, it fails to earn credits to the author's benefit under paragraphs [royalties and subsidiary rights, but not remainders or deep-discount sales] of this Publishing Agreement of at least $x (the "Revertability Floor") in each of two consecutive royalty reporting periods. If the Work becomes Revertable, Author may at any time thereafter terminate this Publishing Agreement by sixty days' written notice to Publisher. Author's failure, for any reason, to so terminate this Publishing Agreement shall not operate as a waiver of any future right to do so. The Work shall remain Revertable only until Publisher issues an accurate and timely royalty statement to Author, as provided by paragraph [] of this Publishing Agreement, showing that the Revertability Floor was exceeded during the preceding royalty period.
This shifts the inquiry to the correct one: Is continued publication of the work commercially viable? The argument then becomes the correct value of the Revertability Floor; I've had decent success suggesting that this number be around 10% of the per-book advance for works of serious nonfiction. And this clause can continue to use "out of print" if the publisher is incapable of changing to accurate terminology. (Or, I suppose, if the author is a Luddite curmudgeon.)
All of that said, I find some comments reported on GalleyCat concerning fiction more than a bit disingenuous, and indeed downright ridiculous.
... S&S CEO Jack Romanos ... said that in an ideal market the only books he could envision going out of print were time-sensitive works such as tax guides — and that fiction titles especially should never go out of print. That opinion was seconded by HarperCollins president and CEO Jane Friedman.... "No. In one word, no. There is no reason for a fiction title to go out of print, because you never known when there is going to be an audience for that book," she said.
The key assumption: That the market for books works in a rational manner, let alone is "ideal." It isn't. Further, in my experience many fiction publishers inhibit the sales of backlist works because they refuse to support them, and all too often actively undermine them. This isn't necessarily through some evil conspiracy (although I've seen a couple of those, such as setting a print run of 2,500 for a book with a six-figure advance after a dispute with the author); it's merely a recognition that a publisher — like any other business — sometimes screws up, and always has limited attention and resources for the stuff that isn't shiny and new.