I think Yoshida coming up is the least likely scenario to be honest. I wouldn't be shocked if we've seen Yoshida take his last swing in the majors for the Red Sox.
I think we'll make do with what we have (barring injury) until we can call up Mayer to replace Hamilton if he's still struggling and Mayer has kicked on at AAA. Can't see that happening until after another year of control kicks in. Grissom could be brought up earlier instead, but his defence just isn't good enough to cover the positions that Hamilton does, so I don't see it. My feeling is Grissom builds value in AAA and is moved. If Mayer is blocked (and he currently is bar an unpalatable utility role), this kid got no chance.
Anthony could be called up much earlier, but the longer it takes, the more it make sense to hold onto his further year of control, also.