I guess the common law relationships would qualify as "something new," since not everywhere has those available yet.
I think you would still need more than independently constructed contracts for each one, though. Not everyone will understand the options, lawyering up isn't very romantic and we can't risk the quality of the contract being linked to the price of the lawyer- that defeats the whole point of equality.
It is also needed for other institutions: hospitals, for example, will need an easy and reliable way to know who gets visitation rights and power of attorney without trouble, schools will need to know that the stranger who arrived to take away a kid is really one of their parents, and so forth. I don't think any modern society has properly explored the complexities yet, and so geared toward two-person relationships as society is we're bound to have blind spots setting us up for unexpected outcomes.
__________________
| (• ◡•)| (❍ᴥ❍ʋ)
|