Pitchers and "their" catchers
 

Have a slight increase with a pitcher's attributes when they pitch to "their own" catcher.

This is an intriguing idea to me.
I've always been fascinated when a great pitcher especially always pitches to a back-up catcher who becomes famous mostly for being the personal catcher to a HOF'er. (See Greg Maddux and Eddie Perez.)

Not sure how this would be incorporated into the game but I would certainly think it would have to involve a relationship building over time. And I would hope that personal catchers would tend to be players who didn't provide a great deal of value other than strong catching skills and a great rapport with one important starting pitcher. There should be some trade off in developing a personal catcher and inserting him into the lineup every 5th game or so. In other words, I wouldn't want a Mike Piazza-type to earn this distinction.
How do you balance out a small bump in performance then for an already great pitcher getting a boost from working with his personal catcher? I suppose the bump would have to be pretty subtle and if there are games where that catcher isn't available there should perhaps be a bit of a negative impact to the pitcher?

(I'm thinking primarily in terms of fictional play as that is my main bag. Even though I'm giving real-life examples. But also intriguing would be how to incorporate IRL examples of this, like Maddux/Perez.)

Well, on player strategy for a SP, you could add in.....they could add in a “designated catcher”

Other designated C’s were Tim McCarver with Steve Carlton.

Interesting idea but how would OOTP handle it?
If designated catcher is injured does pitcher miss a start? If not does his rating go down. Are there any stats that show what affect it has on the pitcher to have a different catcher? Is there any list for historical that list pitchers/designated catchers?

How OOTP would handle it? Could be a check box in the strategy setting for P or C.

Why would a P miss a start?? It's a "preference". If you don't have a backup in your depth chart do you play a game without a SS??

Stats? Easy. Look at the CERA. Most P's who want a designated C will forego offensive prowess for defense and pitch calling.

Not sure if there is any historical list. However, with the entire interweb, I am sure that some poor slob has already done the work.

Few pieces that may tie in here...

First, maybe a preferred catcher gives a slight ratings boost to the pitcher? It might also be an interesting idea, assuming it's not been done already, to track cERA by pitcher, just as you can see how an individual batter fares against an individual pitcher.

Second, this might be something good to tie in to coaching ratings... pitching coaches may work primarily with pitchers, but the catcher becomes an extension of the coaching staff on the field. Lots of times they help manage the defense, for example.

Third, tying in to the second point, maybe a separate metric or measure for a catcher's in-game "intelligence". So not only do you have a catcher's arm and his defensive rating, but you also have a rating that measures how well he manages pitchers/defenses/etc. (You can take this a few directions...)