Password management already is to basically that extent and the tools to copy that information around, backup, etc. also have come into existence to support usage beyond a single browser install.

That's half true, password management piggybacks on top of a system which doesn't have these characteristics, so it means no special work needs to be done on the development side to support them, and it's activation function is only determined on one side of each edge (the user side.) For this cert system to work, you have a bit of a chicken-and-egg problem since it requires both sides of the user-service graph to have done work pre-emptively to support it.