While I understand the impulse, it seems to me that the continuity insurance such arrangements provide is likely to be outweighed by the awkwardness and hassle. For one thing, it turns your current honcho into a lame duck, allowing the media to openly speculate whether the heir apparent would have done something differently whenever things go badly. They say the most popular guy on a college football team is the second string quarterback. I have this feeling he will be bypassed by the designated successor wherever such schemes are adopted.
For another thing, formally naming an heir apparent ties a team's hands. Sure, it's nice if your old man chooses a successor, but what happens if the old man ends his tenure in disgrace? Do you throw the heir apparent over the side too? Does he have a contract that needs buying out as well? And even if that doesn't happen, what do you do if some stud coach suddenly becomes available two years after announcing your line of succession? Are your boosters going to be happy when you name Buck Coordinator your new head coach three weeks after Pete Carroll suddenly decides he doesn't like Los Angeles anymore? I kinda doubt it.
Thankfully no baseball teams have gone this route recently. The last time I remember it happening was when Marge Schott named Ray Knight to be Davey Johnson's successor with the Reds back in the mid-90s. That didn't work out -- replacing Davey Johnson never does -- and I don't remember anyone being all that happy about it to begin with. Joe Torre tried to do it in New York, but he never had buy-in from the front office on Mattingly.
This morning Terrence Moore of the AJC asks Braves Chairman Terry McGuirk how he feels about such an arrangement. Thankfully, McGuirk takes a pass:
"It never crossed our minds. We’ll have to deal with replacing Bobby someday.Thank goodness. I love Bobby Cox, and I know he's not going to be around much longer. But when he does have to be replaced, I want the Braves to think about who's best for the Braves at that moment in time, not simply insert who they thought would be the best two years previously.
It’s incomprehensible to think about dealing with that right now . . . It really
does seem odd when hierarchies in sports are set up so transitions are already
in place before they actually occur."