I was thinking they'd want the weaker bat catching. Probably too soon to definitively say Endy is the weaker bat, but if Bart keeps this up he would be tough to surpass. Of course, they'd be confined by the whole having to have the ability to play first base thing. Not that it's stopped them from putting a guy in the certain position in the past *cough* Cruz *cough*.
Rodriguez has played first base in the minors sometimes when he's not catching. Not a lot, but maybe 10-15 times a season.