Our KD is a good friend, "uncle" to our kids, part of our extended chosen family, and our contract that we drew up for conceiving child #1 did deny him all rights and responsibilities. (And his parental rights were terminated for #1, and the plan is the same for #2, where we didn't do a contract). If you're going to go through with a termination of parental rights anyway, it doesn't make sense to me to to try to come up with some interim legalistic language that could only complicate things at the point where you'd want to start the second parent adoption process (potentially within a year!) if your kd has second thoughts or becomes too invested in having some sort of legal relationship.
In these ways of creating families I recognize that situations are different, but to me, the building blocks of involvement of a kd in a kid's life are trust, mutual respect, and lots and lots of conversation, not the legal or legalistic language. I have known of a couple of situations that have gone sour, causing lots of heartbreak and expense, and from my admittedly biased perspective, something like court-mandated visitation until age 18 or so is much more risky and life-changing for a two-mom family than the threat of denying access is for a kd (which could be heartbreaking if he thought of himself as a dad to the kid, but he wouldn't necessarily have to stay in one geographical place and otherwise be legally compelled to structure his life around proximity to a legal adversary).
Sorry I didn't answer your question, though! We are in upstate NY, and have a lawyer for 2nd parent adoption and wills and things, but I'm not sure if she has experience with known donor contracts--if you pm me I can pass on her name so you can check if you'd like.