The Rays haven't committed to Evan Longoria breaking camp with the major league team because he's never slumped. Rays Index believes this is a good thing:

This is not the first time that the team has stated their concern over the fact that Longoria has yet to experience a slump as a professional. Let's gloss over the fact that Longoria actually did struggle a bit when he was first promoted to AAA Durham last year.

If this is the biggest concern the Rays have with Longoria, then they have no concerns. "He has never slumped" is not a reason to keep somebody in the minors. "He can't handle curveballs" or "He smokes too much weed" are reasons to keep somebody in the minors. "He is too good" is not.

With luck, he won't slump until sometime in his 30s.