I see no reason to even think he'll move out of the lineup for the near future. Magglio or Guillen may have to occasionally DH, but with the Dmitri Young's mostly dissappointing season, I think Shelton has as much chance to play 1B on those days as Dmitri does.
A very distant X-Factor is Carlos Pena who is starting to rediscover his swing in AAA, but I think he only becomes a factor if Shelton or Dmitri have to miss time.
I find it hard to believe Dmitri will be easy to trade with the contract he has. If we do trade him, I'm not holding my breath for getting much useful in return. My guess is that we are already looking for possible trades involving Dmitri. Regardless, I expect this team to find a way to make Curtis Granderson a regular by the end of August. He still has some more development to do, but he has shown enough at AAA to warrant doing some of that developing at the major league level.