The Fediverse Passport would be the central account for all users on the Fediverse.
How it would work
a. Upon signing up for the a platform on the Fediverse the user would be redirected to the "Create your Passport" You would create your unique username. Once signed up you would then have an account on every platform connected to the Fediverse.
b. If someone friends/follows you on one platform they would automatically follow you on all platforms. Insuring that communities and friends could stay connected across platforms.
c. The passport for the user would show your feed on all platforms and allow you to selected which platform you want to see your feed from, also allowing you to directly search your content so you could find a post for whatever reason you need.
d. For the subscriber it would show them your feed and allow them to easily find your content.
e. Tons of customization options including the ability to monetize and or set a subscription fee for the video, blogging, and other "arts" platforms.
Safe Guards
You would be allowed to set your privacy setting to, Public, Subscribers Only, Approve Subscribers, Mutual Friends only, Private (Requires link)
Benefit
Would allow stream less interaction across the whole Fediverse and really get it going. No more having to create a different account on each platform and now you can claim an identity and keep track of your communities, also each site would directly help "advertise" the others.
A passport in the way described here doesn't need to be centralised. Your profile could link to your other profiles through metadata, rather than a centralised system.
And further - the establishment of a single, fediverse-wide account for each user would make it far too easy for those so inclined to silence anyone they wanted merely by banning their one and only account.
It's not a matter of how ones profile would be accessed, but how it would be created in the first place snd how it would be managed.
Necessarily, those who implement the creation of accounts have control over how they're created, who is allowed to create them and how they will be handled after creation.
Any scheme to establish one "central" (your own term) account for the entire fediverse will necessarily be managed by one "central" service, which means one "central" authority over account creation and management
You can't have a full round robin of duplication. In order to have duplicates, you have to have one central original, of which all the rest are duplicates.
And that's exactly the sort of thing the fediverse is intended to avoid.
Every instance is federated but ultimately separate. The accounts on those separate instances are necessarily also separate. There is no possible scheme by which those necessarily separate accounts can be consolidated that does not involve, at some point, some central authority to implement it and/or manage it.
Unless what you are describing involves some type of Decentralized Identifier, let's please stay away from any solution that depends on a single point of failure.
I like the concept, but personally I see the decentralised nature of the Fediverse as a benefit rather than a hindrance, and moving all identity functionality to a centralised system would create more problems than it solves.
Suddenly you'll have a single point of failure for the entire Fediverse. A very appetising target for hackers and DDOS attacks.
An alternative that's in the spirit of your idea would be to allow for auth delegation, i.e. if you sign in with an Activitypub ID rather than a plain username, redirect to that instance to sign in then redirect back to the instance you started from, auth token in hand.
The nice thing about this approach is it's basically just OAuth 2. It's familiar, simple to implement and built in to a lot of web frameworks already. The only extra step would be advertising the server's auth URL via the nodeinfo endpoint, which is fairly trivial to do.
It's like everyone forgot about open ID but also having accounts tied to the an instance is not the problem with good export and import. Communities are what we need to have abstraction on just like IRC if I go to @games i should see threads from all instances on the network. Just like everyone in an IRC network can talk in the same channel even though they connect on different IRC servers.
What Fediverse could use was some kind of equivalent of Linktree. "Here's my personal accounts on Fediverse. Here's some related to my projects. Here's some other random links."
Because currently I'm like "maybe check out my Mastodon profile, it has links" - it works, kinda, but I'm not sure it's the best solution. For example, you could include support for this in the fedi software, so once you specify where your link page is, it'd pull the links and show them on your profile.
...I know, this would be too beautiful for this world and it'd get run over by spammers. But for glorious few days we'd have sensible Fediverse profiles! Think about it!
There is also KeyOxide with solves part of it via cryptographic verification and I believe some fediverse platforms already support it: https://codeberg.org/keyoxide