I think one thing people are ignoring in all this is that there's some serious albatross potential in moving Ryan Zimmerman to 1B. He's not like an AMAZING hitter. He loses 1.5 wins in positional adjustment moving there. He would have ranked 6/8 in wOBA out of qualified NL 1B last year. I've seen no evidence to suggest that moving to 1B magically makes you a better hitter. I guess it's possible, but it's still supposition.
It would probably be best for the team to keep him at 3B if he really has his throwing thing solved.
I'll add to that, that the skill sets for third base and first base are almost totally different.
You wouldn't think of letting LaRoche play third base. But LaRoche is an elite first baseman. There is no evidence that Zimmerman would be anything more than an average first baseman. Granted, fielding at first base is less important than any other position, but it is a factor in this whole equation.
