The bigger picture with the rotation - barring a trade is probably more in the ballpark of:
Guys who are here now: Porcello, Miley, Buchholz, Masterson, Kelly
Guys who could take some spot turns: Escobar, Barnes, Wright, Johnson
Guys who could be here later in the year for real: Owens, Rodriguez
Frankly, even if Owens or Rodriguez might be better than Kelly or Masterson this year, the sort of innings limits that younger guys have these days would preclude them from making a strong big league contribution until June at the earliest anyway.
IMO the odds are very low (barring health) that the Red Sox will be sitting here in June or July legitimately out of it to the point that they'd absolutely won't be buying starting pitching.