Another requirement would be that the current owner of the patent be kept on file and up-to-date otherwise the patent gets automatically invalidated.
As it stands right now it can be literally impossible to find the current owner of a patent. The "inventor" is irrelevant metadata in a patent filing. What matters is who owns it and what happens a lot of the time is some business owned a patent and it folded. Or the patent was secretly sold to some other entity and that sale was never disclosed to anyone (and even if the previous owner can be found they have no obligation to tell you who they sold it to).
So even if you wanted to negotiate a license for an existing patent it's an uphill battle a lot of the time to even figure out who you need to talk to. It's an incredibly impractical system.
As it stands right now it can be literally impossible to find the current owner of a patent. The "inventor" is irrelevant metadata in a patent filing. What matters is who owns it and what happens a lot of the time is some business owned a patent and it folded. Or the patent was secretly sold to some other entity and that sale was never disclosed to anyone (and even if the previous owner can be found they have no obligation to tell you who they sold it to).
So even if you wanted to negotiate a license for an existing patent it's an uphill battle a lot of the time to even figure out who you need to talk to. It's an incredibly impractical system.