If Drew does start slowly, why would Farrell stay with him while knowing that this team needs all of the offense that it can get now?
I seriously doubt that Farrell will play Drew at the expense of the team offense. If Holt stays hot then he has to play as much as possible.
In addition to the SS platoon we have been hearing about, Holt can spell Pedroia now and then. In fact, I say start giving Pedroia time off sooner rather than later because I suspect that the wrist injury is lingering and as a consequence, his hitting ( especially power ) is diminished.
There will be plenty of playing time for all concerned. As I said above, these things tend to work themselves out. There is no use wringing our hands over this matter now.