All of that can be solved with a good lawyer and paperwork. Wills, power of attorney, medical power of attorney....etc.
First off, that is just plain fabricated. A will can't fix death taxes, like a marriage license does. Govco will take their tax bite, unless it's shared property by marriage license.
You can't replace a marriage license with power of attorney.
Nevertheless, show me how you can circumvent the 60thousand laws regarding marriage license privileges. How many different types of "power of attorneys" does it take to circumvent the 60thousand laws regarding marriage licenses so that you can legally be seen as no different than someone with a marriage license for everything but marriage tax benefits, cause you can't fix that.