Ramesh advocates McCain making such a pledge in the new issue of NR. The Hotline picks up on the idea with this analysis today:

John McCain is rolling out a souped-up Straight Talk Express, fully equipped with hi-tech gadgets and stainless-steel appliances. But the most notable accessory on board 3/15 in IA was someone he invited along for the ride: Tim Pawlenty.
– As McCain struggles to recapture the magic of ‘00, the Straight Talk might ultimately travel a starkly different road in ‘08. Visibly older and facing a lukewarm reception from corners of a disillusioned GOP, he’s showering attention on the MN gov in what could be an intriguing ploy: Limiting himself to one pres. term and offering up “VP Pawlenty,” not himself, as the GOP’s salvation.
– National Review floated the one-term notion 3/15, noting it would separate him from the GOP pack and fit the “narrative arc” of his career, acting above self-interest. It would defuse the age issue and Pawlenty would lend much-needed, outside-the-Beltway cred. McCain fueled speculation 3/15 in IA, calling him the “leader of the new generation of the Republican Party.”
– Weighed down in ‘08 by his ‘00 arch-nemesis, against whom he once ran as the outsider, McCain needs to make himself, and the GOP, feel good again. Pawlenty might be his much-needed shot-in-the-arm.