It makes perfect sense to do this for several reasons.
Right now, The Mets are trying to decide who should be their 5th starter for the next month. With Bannister still hurt. The decision is between John Maine and Mike Pelfrey.
It looks like Maine is the favorite. He has a bit more seasoning and can slide into the pen if The Mets pick up another starter through trade. Maine himself might end up being trade bait. He could show enough in the next month to be included in a deal for a proven starting pitcher.
If I were running The Mets. I would go with a 6 man rotation for the next month. Here's why..... Let Maine and Pelfrey audition for that 5th spot in July.
The Mets have the oldest starting pitching staff in baseball with Pedro Martinez, Tom Glavine, Orlando Hernandez and Steve Traschel. These veteran pitchers are going to wear down and get tired arms down the stretch. By going to a 6 man rotation atleast into August. You give these older veteran starters an extra day off in between starts.
Going to a 6 man rotation will help you leading into the trade deadline, It will help your veteran starters now and down the road and it will strengthen your bullpen down the stretch once you return to a 5 man and eventually 4 man rotation in the playoffs.