I agree that it would be a great improvement if we could have alternate parent relationships on WikiTree. As you say this is possible on FamilySearch. It is also available on Ancestry for example.
I know there are workarounds by putting links in the bio but these seem like a stopgap measure until WikiTree supports alternate parents.
There are many different cases. As Kathy mentioned there is the case of a living person who was adopted. But there are many other cases also.
I have been working on the profile for a person who was adopted in 1878. As recommended I have attached the biological parents as the parents in the data fields and linked to the adoptive parents and adoptive brother.
There is also the case of non-paternity events. All sources may indicate that the father was one person but DNA could show that the father was another person. In this case should we attach the biological father as the father and just link in the bio to the person who may have thought they were the father and acted as the father?
In a lot of cases it seems inadequate to always link only the biological parents.
As Eric says it would be nice for the CC7 to be able to follow biological parents but also alternate parent relationships.
If alternate parents were supported it would be good to be able to specify which shows up in tree views (like Ancestry does).