I want to caution you, Are you sure you want to make custody automatic at 12? I mean you have no idea where the kid's head will be at that time. His father doesn't have a relationship with him now, suddenly being with him at 12 will not make it happen. Your son will have friends and school and all sorts of things going on by then and to send him back to a virtual stranger is not very happy.
I am in the same boat as you in a way and I refused to agree to anything in the future like that because you never know what will happen.
I do have full custody and will be, moving in June. I am in Oregon and we are quite progressive on these issues. The only way my X could have stopped me was to file and win custody for himself. I was told that this would be true even if we had joint custody. And he would have to prove I was an unfit mother.
In the end he was a turd about the whole thing bt when he relized he wouldn;t win he played hard ball with me on a new parenting plan. In the end he got:
5 weeks in summer
every Easter holiday
half of Christmas one year, all of it the next year.
Each of these holidays requires that he return to the UK 3 days before
the start of school.
and up to 2 half terms if he wants to visit in the UK.
we split transport costs, my son is to have his own phone, and we have to have a computer with instant messaging and camera.
My son is 12.
I wouldn't agree to anything dealing with future circumstances,m except that we would retuen to the present plan if my X moved to the UK.(fat chance!)
It was a long hard slog, and the X has control issues, but in the end I (we) get to move, I get to marry my Beloved, and start a new life out of the wreck and ashes of the one my X left me with.
I wish all the luck in the world, and do hope you don;t throw the baby out with the bathwater.
My lawyer told me once that the state wouldn't punish me for having a child with this man. Be careful, maybe California wouldn't either...