Five seems to be the magic number this week.

Apple (AAPL) still hasn’t confirmed that it’s developing the tablet-size device observers are now calling the iSlate, but that hasn’t stopped pundits from weighing in on its chances for success. The latest entries: a matched set of lists that come to opposing conclusions.

The first was posted on Seeking Alpha by Ernie Varitimos, a technology consultant who blogs under the byline Zach Bass and is building a site called Apple Investor. He offers five reasons the iSlate is already “a failure.”

The second was written for
BusinessWeek
by Ben Kunz, director of strategic planning at Mediassociates and author of the blog Thought Gadgets. He offers five ways the so-called Jesus Tablet could “change the world.”

Varitimos’ five reasons it will fail:

1. No mass appeal. It’s less portable than an iPhone and less useful than a MacBook
2. Features versus cost. Any device rugged enough to be used as a tablet would be prohibitively expensive.
3. Application schizophrenia. Does it run cheap iPhone apps or expensive OS X apps?
4. No subsidy means low margins. If AT&T subsidizes it, it’s too expensive. If AT&T doesn’t subsidize it, it’s too expensive.
5. It must be a must-have. “If this isn’t a life style changer,” writes Varitimos,” it’s a no-go.”

Kunz’ five ways it will succeed:

1. Magazines and newspapers. Publishers will flock to Apple’s tablet to recapture the paid subscribers they lost to the Web.
2. Concurrent media usage. The device will display TV programs itself, but will be even more popular as the thing you pick up as soon as your regular TV starts showing commercials.
3. Augmented reality. Expect apps that provide instant instructions, product reviews, job histories, sports stats, even the criminal record of that cute guy or gal you meet at a bar.
4. Two-way video. A tablet with built-in Webcam could make video calls as easy as holding up a mirror.
5. Telecommuting. When Apple make portable video truly accessible, writes Kunz, business trips may be a thing of the past.

Varitimos and Kunz both wrap up by saying they could be wrong about the tablet. Both plan to buy one.

[Follow Philip Elmer-DeWitt on Twitter @philiped]