UPDATE: Expect to see Shelton in Seattle tomorrow. No word on who will be sent down.
With the M's going to a four-man rotation for the next little while, this move was hardly unexpected. Shelton brings them another bat on the bench to replace the ailing Mike Sweeney, and Jason Vargas (who seems to be the consensus pick for demotion) will be able to keep fresh as a starter in Tacoma. What'll be interesting to see is what happens with Shelton once Sweeney's eligible to come back. Ordinarily you'd re-instate the guy who's been here all season, but given that Sweeney's probably made a greater contribution off the field than on it, I don't think anyone would be surprised if the M's extended his vacation. A guy like Sweeney is nearly impossible to DFA, but you also don't want to see much more of his .292 wOBA in the lineup, so being able to keep him around the team but out of the batter's box seems like it would be an ideal scenario.
Shelton, by the way, has hit .319/.385/.522 with Tacoma, with twelve home runs and the sort of defense that is most politely described by using zero adjectives. He's here to hit, and if he hits, he'll probably be here a while.